Are you talking premade frames or custom designs? There is nearly no information out there on premades like those from Hi-Light.
There is a lot of information in the other forum on the latter and it doesnt really matter MTB or Road for custom designs. There are a ton of factories to work with for those. The two most popular are probably Waltly and XACD / XATW. The first is more consumer friendly with less options, the second is more B2B focused and has more options. Both have OEM customers, XACD / XATW seem to serve a higher price point and IMO their welds are aesthetically nicer and their machining near perfect, but they also cost more.