aftermarket parts for a project gun

[Merkage21]

hi guys,i a plan on creating a unique gun that will turn heads and make people with systemas and sopmods say"i wish i had that gun!!"but there are a few thing that i am unclear about,firstly ..i was wandering if there is a aftermarket recoil system out there or if it i could send it off somewhere to have someone install it,is it possible,i know people may say why not just buy a sopmod,or something of the sort,but it ust wont be the same,i want build my unique gun fro scratch,with a unmodified m4,

also,i have a m4 with pneumatic blowback,i was also wandering if this could be purchased after market or modded to achieve it,

any advice will help

thanks