Try Ribcraft...01935 411846....
This is my boat, a 4.8 ribcraft, they also do a 4.2 and both boats are based on the searider hull. This cover was made by another manufacturer for ribcraft, I would think it would be a small leap for them to make one for a 4.0 boat of a similar shape/design
My cover was with the boat when i bought her so i have no clue as to how much they would charge. Maybe they would put you in touch with the people that made it so you could deal direct.
Worth a try mebbe
PS...although this picture doesn't show it the cover extends all the way over the outboard too.
Are we there yet?