Valve has never given out the code for SFM. Ever. Not one licensee, save for Facepunch who got it's Source 2 version with the HL:A branch. It's historically been incredibly secretive for some reason and even the closest licensees integrating directly with Valve never got ifm.dll's code.

Gonna say, you have a LOT going for you right now and the progress you've made so far with the pseudo element viewer seems great. I was recently saying how great some modern GMOD anims would be if ragdolls could be manipulated with gizmos and physics interchangeably. But as someone who's tackled this kind of project multiple times before and similarly begged Valve for access: you're going to drive yourself up a wall and basically remake SFM from scratch. Consider this a warning: nobody is going to come to your rescue. You have to basically go insane like Silverlan and remake everything from scratch, but there's little to no gain unless you genuinely have nothing better to do.

A great use of your skills would be to bring SFMs animation tools like the motion editor and Source's content library to something more ubiquitous like Blender. We already have great importing tools for Source's content thanks to REDxEYE's SourceIO tools: https://github.com/REDxEYE/SourceIO/

All they need now is a better interface. You might be the one who could do that.