Hubcentricity again, anyone know of any ring suppliers?

I had some 15" wheels on my car the fit the bosses the front and rear perfectly. I needed different offsets, so I bought some "Corvette" 15" wheels from Wheel Vintiques. The offsets are just what I needed, but the bores are larger, is that the "Corvette" difference? So, my wheels are being located by the lugnuts. I know on modern cars, that's a terrible thing to do, especially front wheel drives. I'm guessing it has to affect these cars somewhat, too, huh?

If the larger bore is a standard size, and my bosses are a standard size, there ought to be some pre-existing off-the-shelf hubcentric rings. Anyone know of a supplier who does that?