Your just going to have to hit the regular parts kits sources till one shows up.
That was how I built my BIG TROUBLE IN LITTLE CHINA gun.
Was pretty shocked it ran 3 diiferent mags without a single issue.
Haven't shot it since.
Right now thanks to 3D printing the complete kits like I bought are valued a bit higher then a working complete gun since there is no paperwork or BG check.