The cold rolled round stock shouldn't be that expensive. Call around to the junk yards, most of them have this common shape. You might have to scrounge around in the pile, but it definently isn't expensive. Be sure and don't choose hot rolled because this stuff doesn't have an accurate OD. If your cold rolled has been outside and has some rust on it (not heavy rust) just take some emery cloth and take the rust off! The compound isn't that hard to find either. It is pretty much the same as valve lapping compound, find it at good auto supply houses.
One other thing to think about: you don't want to lapp too much! I read somewhere, I think it was Greybeard.com, about a fella that got carried away and after he was done lapping his rings wouldn't tighten up, but I think that would be a very rare case.
