Hmm, think those calipers need more than just degreaser. I'm sure I've read of restoration jobs where such things were brought back to pretty new-ish standard. Sand/shot/bead blasting? (obviously with suitable precautions taken to protect fluid ways, piston bores etc?) Check classic bike type magazines and sites, they usually have such services advertised, might be worth it.
If you're going the 2nd hand calipers route, you might try Partfinder UK. They have a number of breakers on their books. You phone them with details of what you're looking for plus name and a contact no., which they pass on to these breakers, who then contact you if they've got what you want, and tell you condition and what they're asking. you just take the details if you're not sure and can call them back later once you decide - no obligations. Can't seem to find a web address for them, but phone no. is 09060 300123.
