I am looking for something that may or may not exist

[Hirschkopf]

I'm a fan of the Springfield Armory Saint Edge PDW. Here's a review and some details on how they put it together; maybe some of it could be inspiration for your project:
https://www.gunsandammo.com/editorial/springfield-saint-edge-pdw-ar-pistol-review/375352

 

[bushmaster06]

Stock options are limited as most will use the buffer tube for support. So you can use a shorter buffer tube using the DFA option listed below, and there are seveal others. You can also go MPX stock and and a picatinny adapter that replaces the buffer tube. You can then use a BRN180, JKL upper or any short barreled piston driven upper like the Adams Arms. LAW Tactical makes a modified bolt that lets you run any upper you want with no buffer. Evolution Systems does too but its backordered.

https://www.midwayusa.com/product/1022440015https://www.strikeindustries.com/si-stab-mpx-mcx.htmlhttps://deadfootarms.com/products/dfa-modified-cycle-system-rifle-caliber-ar-pistol-kit
Uppers and bolts

https://www.midwayusa.com/product/1019608491https://www.lawtactical.com/ar_internal_carrier_ARIC_p/99367.htm

I think it was Brownell’s that I got a pistol buffer tube from that was the outside diameter the whole length of the tube so I could cut it shorter and run a threading die. I’ll upload a picture later.

 

[OKNewshawk]

Dead Foot Arms is what you want. They make a 2.5 in modified cycling system buffer that you can put a SCW extendable stock or brace on it. If you are a veteran, you can also get a lifetime 10% discount after verifying your veteran status. SCW25-STOCK-RC-GEN2

 

[bushmaster06]

Here’s my SB Tactical that I modified. I could probably cut the tube down another 1/4” and you could probably cut the part that supports the bars shorter if you wanted, but it might sacrifice stability of said bars. I also cut more notches in the bars for they collapse further in.

I think if paired with a piston upper or the special BCG you could chop the tube really short.

 

[bushmaster06]

@kingfish