I didn't want to hijack Piosad's thread but I've done the same and lost a key to what I think is a very good lock - looks like a heavy chain for motorbikes but it is very light and the lock part swivels so dead easy to get the key in regardless of chain position.
This happened a couple of months ago and the bike, which was abandoned by a previous guest, has remained locked up since as I was hoping the key would turn up somehow and I can't bring myself to destroy a good although useless-without-the-key lock.
The lock originated in Belgium, I think, and has 'Bicycle Gear' on cover but I don't get far on Google with that. Had wondered if I could order a replacement key.
Maybe the lock is not as good as I think - I'm just going on how it looks after all - and I may just have to bite the bullet and chop it. The bike itself has been great for around town and even further afield and I've really deprived myself of it's use for the loss of one little key so this is a last-ditch attempt for a solution: maybe someone here knows more about the type of lock described or has some miracle solution?