Dave, there are flatbolts, roundbolts and hollowbolts to consider.
The 6mm is the scarcest short-action flatbolt, followed by the .243Win.
I've never seen a long-action flatbolt in the V, although theorhetically there should be a few out there.
Hollowbolt Vs are also rare. All the hollowbolts are long-action. I have one V in .25-06. It's the only one I've seen.
In roundbolts, the .280 is the rarest. The rest are fairly common, even the 6mm, although the most common are the .22-250, Swift, and .243Win.
Hope this adds some clarity.
Jim