DarkAhrix

https://www.aliexpress.com/item/32792113198.html?spm=a2g0s.9042311.0.0.27424c4dbMaSAK

I got this for the b30+31. worked well with my Cyma 105, though i had to file away some of the top rail to fit past the flash hider detent, and it could probably do with a spacer or shim inside the receiver but in general fits pretty well.

Otherwise i'd look at Bunnyworkshop, where i got my asura m4 stock adapter, but they also sell the zenit stocks, top cover rail and such. http://www.bunnyworkshop.com.hk/airsoft/index.php?route=product/search&search=Asura

how it turned out - still haven't really decided what flash hider to get: 

just got a lct 105 and priced all parts at £395