I purchased Master of Magic. I now have a new computer and wish to have this game on it. I don't mind paying the additional $5 at all! However, it tells me that I can only buy the second copy as a gift. Any ideas?

You don't need to buy a second copy for that, you can install the game on as many of your computers as you like.
Gog doesn't have the kind of restrictions Steam has.
Just download the installation files on your new computer and install the game there.

With GoG, you buy the right to use your games on any and all of your own computers. You don't need to buy it again. Just download the installer to the new computer.

In fact, now that you've purchased the game, there's no worry to ever losing it either. If for some reason the game was removed from sale, you'd still be able to download it.

My GOG is infested with user scripts, so screenshot won't help you...

Basically you want to hover over your account menu, then select "games".
Then click on Master of Magic.

Now you can a)
- Click the big blue button, This will download and install the Galaxy client and the game (if you know Steam, it's similar)
- Click the "Download Offline Installers" button and then "Masters of Magic". Once downloaded simply run the the file downloaded, it will install the game.

@jhonmill987: wait, what? What gmail support lol...

Is that a riddle or what?