I bought my StarTech full size frame rack on Amazon, since it was cheap and disassemblable. Ditto for network wall rack in the basement, made in Poland. There is a type of music rack on casters which is also good for short equipment, also Amazon. Apart from that it’s eBay and local used equipment sites. Mikrotik is cheap enough to buy new.
What are your specific needs? Mine are low-power and low-noise or passively cooled for 24/7/365 stuff. Everything else is free game, since it never runs long enough to matter much.