There is a shop in Canada that works on Renaults and their gearboxes (
http://www.alpine-america.qc.ca/). I have heard that parts are not readily available for the Renault gearboxes used in Europas but that may have changed and he may be able to help you. If he can, be aware that you will have to arrange shipping including customs both ways. I contemplated this for my tranny and gave it up. Shipping by truck from NC was over $400 and getting the customs taken care of was at least $100 each way (it may have been $200 each way). It was also a lot of trouble so I'd be surprised if there were not an easier way to do this but I don't know it.
As Cal says, there maybe some shops that work on these trannies. If someone doesn't post a good shop, a call to Dave Bean or Ray at r.d. enterprises may help. There are occasionally people willing to sell their trannies so posting the the lotuseuropa yahoo group may help. This would be the best route.
Failing all that, the NG3 is probably the way to go. Richard at Banks Service Station (
http://www.banks-europa.co.uk/index.php) sells a kit but it may require a new rear cross tube. Again, the yahoo group has several people who have done NG3 installations and somebody there may be able to help with design and parts that you would need. NG3s are pretty easy to find at
http://car-part.com/. Steve Veris (steve.veris@sbcglobal.net) has them from time to time. People have also worked up cable shifters for NG3s, too. I think if you have to go the NG3 route, it will require a fair amount of modifications no matter how it's done.
Good luck!