Thats news to me. All the garages I've used have been happy to use parts I've supplied.
what happened to this part?

Do it yourself. LEARN.
Followers of Elvi would know from my posts that there have been occasions where I have had to use my local garage, as a last resort.
The only two were:
1. siezed caliper at MOT time. I got a new one, they fitted it. Then completed the MOT
2. I had purhcased new Brembo pads and discs, and a full exhaust system. Not having a ramp, it only made sense to use my local garage fit them all at the same time. This in no way say that I am not competent to do the jobs myslef.
In point of fact, I have done all these jobs when previously I had access to a ramp, so nothing for me to learn.
As my local garage is owned and run by a school friend, I know I get a good service.
Jonathan.