Larry Stock's 'Pantera Part Connection' sells fully rebuilt stock Girling calipers on an exchange basis. Some bleeder valves have different thread sizes. Porsche for example are around 7/16" dia (fine thread and of course metric). I believe Dorman stocks them at some NAPA stores Take one of yours with you & compare threads- a counterman will help you.
ALWAYS use a 6-point socket wrench to remove stuck bleeder valves. Which happens when brake or clutch fluid is not changed yearly, as it should be. The rear calipers seem more prone to get stuck Open end wrenches very often spread under pressure and round off the valve's soft hex head. Expect to break off some frozen bleeders and/or bend/break some little open end wrenches. The price of 'deferred maintenance'.
If you're so poor that you don't own such a socket, put the correct little open end wrench on the valve, then clamp a Vice-Grip pliers across the wrench's open ends to keep the wrench from spreading. Use both the wrench handle PLUS the pliers to unloosen it. Be very careful drilling out broken threads as the valve seals off against a conical bottom of the threaded hole and it's taper is different than your drill end. Also, once the valve is out, look thru it: I've had valves that were so varnished up that I needed to DRILL them out to reuse them!