Cant seem to find anywhere that sells them. They are a large size - around 15mm. Had found some 15mm sportsmatch ones at tawnado.com. Had a chat with them though, they said the angle is too sharp on the rails for their type.
Any tips on where to get some would be really appreciated! Will probably try John Knibbs in the AM. Itching to get a scope on my "new" .177 mk1.