I saw two or three 7.8 Ribtecs on the Hamble last weekend while out teaching if this is any use. They were all out and about on the river so not sure where they had come from.
Also was in Solent Honda's yard at Warsash last weekand they were loads of Ribtecs in there on the shore. Most were 6.5's but I'm sure I saw a 7.8. May be worth giving them a call.
Otherwise Ocean Quay Ribs in Southampton usually have one or two kicking aroung in their workshops and yard in the process of being fitted out and Southampton University have one at the Oceanography centre.