I also looked around even with 2000lb lots, and the only refiners that could pass the smell test wanted 1000lb of RAM sticks only - in their definition that is 'high grade escrap' (which caused problems in the conversation because high grade boards in the scrap industry is old Pentium and before boards).
The costs and fees for any motherboard refining would eat up the total revenue from the melt, so unless you have large amounts of ram, pre-P4 processors, or a half ton of gold fingers I have not found a way to profitably send material to a refiner.
If you find someone trustworthy that is backed with insurance, paperwork, and won't shut down and walk away with your metals, please let us know because they could probably get a lot of business from the forum members.
Otherwise, follow the knowledge and experience of the forum and know that small scale refining of the best quality material is probably the only way to make a profit vs just selling to the escrap industry.