where or what from can these be sourced from for mid engine bike engine project

you could always make your own.....this is the rear end of a heavily crashed GT1 going back together, Ive used MKindy uprights with a few mods and made my own wishbones, this pic is the 1st fit and there a fair few more bars too go in when diff and drive shafts are fitted.
Rescued attachment arseend.JPG

You have U2U