New to the forum so go gently on me.

Does anyone know where I can get a front caliper at a reasonable price. My pistons are stuck fast and will note move even with great pressure behind them.

Where do you live?

You tried with pressurized air, right?
I would go hydraulic - can you pump the piston(s) out via the master cylinder (hand lever or foot pedal) on the bike?
More force and less danger ...

Andy

and don't make the rookie mistake of pumping them out with the original master cylinder only to find the unstuck one comes out leaving the most stuck side.
Put a steel or wooden packer in the caliper aperture to let both pistons come out equally...

Tried air pressure and high pressure (2000 psi) electric grease gun. No movement.

Push them in slightly first with the correct tool.

Might be good to take the seal off, clean, dip them in rust remover for a couple of days first.