When you make these calls, ask for either the RMA department, or Tier 2. Tier 1 is useless for anything that isn't software/flight log related. They'll tell you they don't have parts, or that you need an entire XXX kit. I've experienced this twice.
However, once you get someone from the RMA department, you should be fine, and able to buy whatever parts you need. Per someone else' suggestion on this board and the FB page, I was able to source some cables that Tier 1 TS claimed don't even exist. I paid .75, and they paid the FedEx to get it to my hotel.
Seriously, 3DR's tech support rocks, but who ever is responsible for training/sourcing the crew in Tijuana needs a bit of training/redirection from the San Diego team. Once you get someone from San Diego on the phone, all your worries will likely go away.