I built mine out of Faztek T Slot. Doors on all sides. The 80/20 lift off hinges were really expensive, but I can just lift the two front and two side doors off if needed. I cut sheets of 1/2" cutting board and mounted in the rear to hold equipment. On the upper right I mounted two pieces of T Slot. The UV is mounted and hanging from one, and the algae scrubber in the front corner is suspended from the other. Right side is a sump with filter roller, skimmer, etc. Left side is top off. The sump has return and feed bulkheads in the rear. The cutting boards only come down to about the height of the sump and ATO so the bulk heads stick through to the back with 90 degree barbs facing up. 1" black hose connects everything to up top.
To answer the question. T Slot, connectors, bolts I got from Amazon. 80/20 sells there. Got some other brackets and the hinges from Ebay. 80/20 sells there also. Since the Faztek T Slot has gotten a lot more expensive, the last time I needed a piece to mount the UV, I ordered directly from 80/20. Only problem with that is the amount of shipping they charge.