I've seen them on both an Aston Martin (DB3S?__not really up on all the AM racing models...) and a Ferrari 275 GTB-C (Competitzione), so apparently they were available from Dunlop as well as Borrani.
When I replaced the wire wheels on BN6L-942, I tried to get the polished alloy rims, but Dayton was no longer able to "punch & dimple" the spokes holes like they once could, so settled for the (chromed) steel center-laced set. I saw a set of Borranis on a BN7 years and years ago, and they were beautiful.