Parts source? (Small Business Optiplex & Precision)

Is there a third party parts vendor I can use to purchase Dell factory parts? Dell has been horrible (Dell Spare Parts by Phone) and I'm looking for easy simple things.

Is there a way I can buy directly from Dell or is there a parts wholesaler that will be reasonable? I have a fleet (50+) of Optiplex 755's (MT, SFF) and a bunch of Precision Workstations. I'm looking for simple stuff like CD/Floppy bay blank/block off plates (to cover the empty hole), Cables & internal parts, misc. hardware like screws & clips to hold motherboards to the chasis, etc.

I'm sick and tired of spending hours on the phone with Dell fighting over Service Tag IDs, Warranty info, etc. I just want to be able to order the parts I want so I can configure my machines the way I want. For example I have a 755MT HDD caddy which lost two of the HDD retainer pins - can I purchase those? I also have about 5 spare "parts" computers that I'd like to consolidate and get running.

Thx for any advice or input. I'm located in NYC if that matters. I'm fine doing things via USPS/UPS as long as ordering is easy.