Hi Andrew, have you tried your local bearing supplier? there must be one somewhere in your area, and if the seal is a simple lip type they should be able to help. Try them anyway even if it's a bit of an odd one. You never know, they might just have one in stock.
Presumably yours is an R2106 with the type 334 gearbox (the one with fourth gear "forwards"). If you look in Parts Book PR953 on page 31.20 (sorry, I don't have a scanner so can't send a copy) there is an exploded diagram of this gearbox. The seal you seem to be after is shown in the extreme top right of the page and is given as 35 x 17 x 8. There is also a little diagram showing its profile.
The part number was 77 03 087 050. This will almost certainly now not be available but it might be worth contacting the Parts Department at Lifestyle Renault in Tunbridge Wells to see if they can provide a trail to a similar item (or an updated part number). They are very good at this sort of obscure enquiry.
Many thanks for that, I was a bit unsure I was measuring it correctly.
Looks like ive found one of the correct dimensions on the der franzose website in the end doesn't appear in any catagory only via searching which is where I was going wrong.