It's certainly an I-17 cable you want........ and I'd suggest it's four pin........... I found this link. It gives what can only be a 'model number' as... USB Cable I-USB17 (39233). That's a US site which may not be much help, but if you find the cable in the UK and check that is has that model number you should be ok.
Alternatively you may find somebody on the Pentax UK Forum that can advise.