What have you done so far to try to fix the problem? Are you planning on doing the work yourself?
I would first try to determine if the problem is in the hydraulic system (normal braking) or if the parking brake cables are seized. Do you have a lot of rust issues in your area? It's possible the parking brake cables can swell inside the sheath and "lock" up the brakes. Do your wheels turn at all, if you have the rear off the ground (on jack stands or on a hoist)?