Who is a good source to send out your 1969 4 piston calipers to be rebuilt? Or do you just go to places like Autozone, O’Reillys, etc for a core exchange? Thanks

Master Power Brakes and White Post Restoration used to be the go to's for re-sleeving and rebuild service or kits
Calipers Online list them.
With any I'd find out is they will rebuild yours.

I'm assuming that your asking about BENDIX 4 piston caliper disc brakes on a B body car?
If so, be prepared as rebuild kits, and especially caliper pistons, are pretty much on the unobtanium list to find, and get, in this modern day and age.
And the prices that you would have to pay are hugh $$$$$$$$$ these days.
By chance if your asking about A body, Kelsey Hayes, 4 piston calipers, i rebuild them.
Jim V.
hemi71x

Those are easy to rebuild ( O rings on the pistons) as long as the main body holes where the piston fit into aren't corroded badly Same thing on the pistons
I did a set on a 1969 Charger 500 years ago, that car was from the San Franscico bay area and needed the calipers to be sleeve due to internal corrosion in the holes where the pistons fit into The piston were fine
I don't remember now who I had sleeve them back east, sorry

These guys did mine 30 years ago Hydraulic rebuilder