Another good place to go look for is churches.
Go visit a few, leave your contact down letting them know if they are going to upgrade, you'll take their old stuff. Very often the old equipment can still be used perfectly.
Cash converters are unlikely. I haven't seen the stuff you're looking for at CC.
Maybe just visit studios, make friends with pro audio shops, tell them that if they have customers upgrading you're willing to help dispose of their old equipment. And if the equipment is still working you'll purchase it from them. etc.
You really need contacts when looking for used stuff, especially in pro audio equipment.
I did see mobile rack equipment at sim lim tower and sim lim square before.