Shooter's Den in Sudbury was a source for brass and cast bullets when I had a Mk.VI, although I got brass from Buffalo Arms in the U.S. back then, before the current export regulations came in. The Mk. VI is the only Webley I've owned or even fired and I don't expect I'd like any of the others as much, but in your situation "opportunity to purchase either or both" I'd get both. If I couldn't afford both I'd get the Mk.VI first.