Not sure if they have 43x options but I've purchased a few barrels/slides from these folks... Great service and pretty reasonable prices...
https://80pbuilder.com/
I was looking at those... I did an SCT/G17 clone a few months back. Felt like the SCT was a pretty decent value. I believe the one I purchased came with the frame parts and trigger...
What parts/brands are you looking at getting?
I recently purchased a 12.5" from Uintah Precision. It's a bolt gun upper that goes on their AR10 lower. Purchased some ammo from Gorilla and currently working on components for hand loading... Which I'm a complete newb at.... Looking at ordering a CGS Group Hekate to utilize the full benefits...