Skeleton receivers for M4

Does anyone know where to get a skeleton receiver? Or am I getting the dremel out? Like this but mainly at the magazine well 1562019640-3_3a1a3774-02e7-4f4b-9b0e-cb507e895b8b_600x|466x466

ruff as guts but get the idea?

That’s the spirit.
I’m about to cut out the trigger guard on a J9 to fit this…