I have a custom mining rack that is made out of welded steel and wood that i think supports 6 or 8 cards connected by risers, and i also have a lot of those, it was designed for the asrock bitcoin motherboard.
https://www.asrock.com/mb/Intel/H81%20Pro%20BTC/I also have that motherboard with cpu and ram if you want, and a 1500 watt server power supply that can handle a lot of cards.