Since this is based on the Quake 2 engine I was wondering if anyone knew of any source ports that exist for SiN.

Modified Quake 2 engine, for which Ritual never released the source. No source ports exist, but it runs just fine as-is.

The Ritualistic fansite does have the older versions of the source code for the game, though I'm not sure if the 110src applies to to the current updated 1.11 retail version since I haven't had time to compile it, though I did looks through it extensively. I'm sure VS2012/13 can reliably convert the project properties, though this was written in VS5 and those tend to end up either buggy or with some unfixable linker errors. Just cross your fingers and hope for the best.

Haven't tried the level editor yet either, but from what I've heard, it still works with a bit of tweaking.

http://ritualistic.chrissstrahl.de/downloads/SIN/utillity/

The SiN 1.10 source is still only one part of the equation, the game. The modifications for the second part, the engine is not there.

I tried using Yamagi Quake 2 (... I cannot post any links at this moment, it's easy to find though) (the reason for this choice is the 64-bit CPU architecture support) thinking I might be able to make it run on Linux by quickly stitching it together, but a more dedicated effort is required due to the unreleased changes to the engine.

I have no interest spending more time on this, but in case anyone is interested I got it loading the SiN-pak files: The difference to the PAK files is simply the magic number ("SPAK" instead of "PACK") and each entry's name is 120 characters long instead of 56 (see src/common/header/files.h and src/common/filesystem.c for the relevant code).

The first thing it complains about then is a missing file "pics/default.pal" (Draw_GetPalette() in src/client/refresh/r_draw.c). After working around that issue it will complain about missing menu commands - at that point I stopped trying.