An odd thread! But is there still a request for such thing and is it a rarity?

So, I obtained a Betamax VCR from a house clearance and inside was a Betamax tape half eaten which is a porn film. After doing some research I can only locate VHS versions but not Betamax, so are they particulary rare? If so, is there an enthusiasts forum for this sort of thing so I can sell it?