aleksej: Hello to all members of GOG community.
There is my first post here.

At first want to say. GOG.COM team don't be offended, but... your MDK package just sucks, imho because it lacks initial DOS functionality. Why you threw DOS part of game?
Saved one percent of package total size? Oh, that great!
Bought it and was unpleasantly surprised.

Ok, now how to legitimately and fully restore all missing MDK DOS files using only public, royalty-free resources on the net avoiding any kind of warez.
Missed files are:
mdk.exe - MDK DOS executable.
mdk95.exe - MDK Windows executable. Optional. GOG's MDK new executables both works just fine in my Windows 98 setup.
dos4gw.exe - DOS protected-mode extender (provide full amount of system RAM, above first megabyte to software).
hmidet.386 - this driver from HMI sound API detect your souncard.
hmidrv.386 - this driver from HMI sound API give you access to "digital" (aka PCM) sound capability of your sound card.

Now there are links.

1. Main executable can be taken from official updates. Thanks god, Shiny didn't has make any kind of patchers, just provided renewed files in zip.
Here is english (USA/Europe) versions of various executables (DOS,WIN,3Dfx and etc.)
DOS:
[url=http://dlh.net/getfile.php?40:e300346db4faa96e:5a7b2c35ab35f768:/pc-patches/general-patches/mdkdose.zip]http://dlh.net/getfile.php?40:e300346db4faa96e:5a7b2c35ab35f768:/pc-patches/general-patches/mdkdose.zip[/url]
All the rest:
[url=http://dlh.net/getfile.php?40:e300346db4faa96e:5a7b2c35ab35f768:/pc-patches/general-patches/mdkw95e.zip]http://dlh.net/getfile.php?40:e300346db4faa96e:5a7b2c35ab35f768:/pc-patches/general-patches/mdkw95e.zip[/url]
[url=http://dlh.net/getfile.php?40:e300346db4faa96e:5a7b2c35ab35f768:/pc-patches/3dcard-patches/mdkd3de.zip]http://dlh.net/getfile.php?40:e300346db4faa96e:5a7b2c35ab35f768:/pc-patches/3dcard-patches/mdkd3de.zip[/url]
[url=http://dlh.net/getfile.php?40:e300346db4faa96e:5a7b2c35ab35f768:/pc-patches/3dcard-patches/mdk3dfxe.zip]http://dlh.net/getfile.php?40:e300346db4faa96e:5a7b2c35ab35f768:/pc-patches/3dcard-patches/mdk3dfxe.zip[/url]
[url=http://dlh.net/getfile.php?40:e300346db4faa96e:5a7b2c35ab35f768:/pc-patches/3dcard-patches/mdkpvre.zip]http://dlh.net/getfile.php?40:e300346db4faa96e:5a7b2c35ab35f768:/pc-patches/3dcard-patches/mdkpvre.zip[/url]
[url=http://dlh.net/getfile.php?40:e300346db4faa96e:5a7b2c35ab35f768:/pc-patches/3dcard-patches/mdkrede.zip]http://dlh.net/getfile.php?40:e300346db4faa96e:5a7b2c35ab35f768:/pc-patches/3dcard-patches/mdkrede.zip[/url]
[url=http://dlh.net/getfile.php?40:e300346db4faa96e:5a7b2c35ab35f768:/pc-patches/general-patches/mdkffe.zip]http://dlh.net/getfile.php?40:e300346db4faa96e:5a7b2c35ab35f768:/pc-patches/general-patches/mdkffe.zip[/url]

2. Royalty-free DOS/4GW lie in Open Watcom free compilator packages. Also exist as separated off of whole package zip file:
http://www.ibiblio.org/pub/micro/pc-stuff/freedos/files/devel/c/openwatcom/1.5/ext_dos4gw.zip

3. HMI* files, required for in-game sound at all.
Human Machine Interface Inc now defunct, fortunatelly needed files still available in some waybackmachine's cached pages:
http://web.archive.org/web/19970225190838/http://www.humanmachine.com/PUB/SETUP40.ZIP
This is free end-user related HMI setup utility package. Take hmidet.386 & hmidrv.386 from it.

All these files copy to MDK root folder.

And some little but mandatory polishing. Original game has simple CD protection and looking for game CD in drive.
As owners of GOG's "CD-less" digital license shut it up with very simple crack which available for various versions:

== CUT HERE ==
M.D.K - DOS net update ver.
MDK.EXE
00030FC1: 74 EB

M.D.K - W95 net update ver.
MDK95.EXE
000010F1: E8 B8

M.D.K - 3Dfx net update ver.
MDK3DFX.EXE
00001CBD: E8 B8

M.D.K - Direct3D net update ver.
MDKD3D.EXE
00001D45: E8 B8

M.D.K - PowerVR 3D net update ver.
MDKPVR.EXE
00001E27: E8 B8

M.D.K - Rendition Redline 3D net update ver.
MDKRED.EXE
00001D41: E8 B8

M.D.K - W95 / Force Feedback net update ver.
MDK95FF.EXE
000016C1: E8 B8

M.D.K - Direct3D / Force Feedback net update ver.
MDKD3DFF.EXE
00001D79: E8 B8
== CUT HERE ==

Save this block to .CRK file and use it with following universal cracker:
http://www.gamers.org/pub/games/uwp-uml/romulus/cracks/cracker.arj

Thats all.

p.s. And sorry for my bad english and questionable solution for a probably artificial problem.

nex01: aww man most of these files are down...
why not uploading everything you need in a zip file and attach it here?

I'm still in need of it to play the game on DOSBox on my Raspberry Pi.

TheAvatar.783: No need to track down DOS executables from potentially dodgy or ephemeral file-sharing sites. GOG provides everything you need; just download the Macintosh OSX version! Rather than trying to get the Windows port running in Wine, GOG instead used the DOSBox (pure DOS) version of MDK.

1) Download Mac OSX version. This will save a DMG file
2) Open DMG in 7Zip and extract
3) In the "\MDK\MDK.app\Contents\Resources\MDK.boxer" folders you will find two sub-folders: these are "C.harddisk" and "D.MDK.cdrom". These are the folders you actually need so copy them to your DOSBox installation. You don't need to extract any of the other files or folders.
4) Mount the C.harddisk as the C-drive
e.g., Mount C "c.hardisk"
5) Mount D.MDK.cdrom as a cd-rom
e.g, Mount d "D.MDK.cdrom" -t cdrom -label MDK.
6) Run MDK.exe from the hard-disk (alternately, you can create a brand new install by running install.exe from the cd-rom)