KG36C to GBB KG36C?

[Kiki]

Basically, no. There is no "kit" or anything of that sort. You would have to take an existing GBB pistol and modify it and your G36 to fit and work in the G36 body/bolt. Even then, unless you did some very extensive modifications, you wouldn't have much blowback. You'd just have a less reliable G36 that holds 25 rounds per mag and has a bolt that moves back and forth. Kinda cool I guess, but extremely unpractical.

Or you could design/manufacture your own GBB system (haha, good luck).

[Thor]

Yeah, I agree with Kiki. Since no one has made any aftermarket kit or anything, you'd be left with 3 options:
Modify a GBB pistol (really f-ing hard)
Modify a GBB M4 (practically impossible)
Modify a GBB AK (still really hard)

What you want is neither practical nor plausible, unless you have access to CAD and the machine shop necessary to make all your parts from scratch.

Basically, GBB guns operate almost nothing like an AEG.