Mark Serbu of BFG-50 fame? I had one of those, wish I'd never sold it
Anyway, it's a fairly small pool to draw from, so I think there's an ebb and flow to what's for sale at any given time - when I was looking almost 2 years ago the -8 seemed to be rare and I ended up with an 8A at least partially because that's what I could find in my price range.
As luddite42 said tail dragger's do tend to be more popular with a certain type of pilot that gravitates to the sportiness and tandem seating of the RV-8 - keep looking - good 8A's come up for sale too...
I dunno - the -A looks pretty badass...