On a new, or newly refurbished Caliper, without the brake hose attached, you should normally be (just about) able to compress the piston into the Caliper by hand, it's a bad sign if you needed a lot of force with a clamp to do so.
If you were in the UK I'd suggest the below, I assume there are similar offerings in the US.
Quality is important though, so I would do some research on brands. 'Bigg Red' has a good reputation, but is UK based.
It's an easy enough job to do, providing you are good at fiddly things.
Btw, BMW say not to lube the slide pins between the Caliper and the Carrier, just to get new ones and install dry. I ignore that on my car though, and use a little spray on copper grease (it's not very thick at all).