I've had similar problems with Dell in trying to organise a replacement heatsink retention module.
I have had other Dell systems in the past and both the system and the aftersales service had always been spot on. However, since they have moved the support to India I have had nothing but problems.
After numerous phone calls, emails and even letters, I finally got through to a company who they outsource biz to for parts to systems which they no longer manufacture - 'Service Centre Europe' (i think that was their name). They are UK based and knew exactly what I was talking about. After speaking with their Customer Service Manager and explaning the prob, I had an engineer on the phone within an hour who identified the component I was after. The part arrived within a matter of a few days.