i had a similiar problem when my cover got holed . i bought one off eBay as Nich shows, for a few pounds together with the micro switches that are used, swopped over the blade , p.c.b. board and chip and all is working, my only reservation is they are not as well made as the originals resulting in you having to press very hard on the buttons operate, but will get you out of a hole.You may consider getting a spare key or keys from a scrap or write off which you could use as a donner for your internals, otherwise it will cost quite a bit to replace with new.