Build it !!!
It’s easy and there are plenty of resources, specifically at AR15.com
I was all set to start building one a couple weeks ago when I ran into an issue I didn’t know existed: only a few receivers take Glock mags without an adapter. Not taking Glock mags is a deal-breaker. So I was back to square one in terms of finding proper parts and I told myself to just buy a complete one. I’ll check out ar15.com. Thanks.