Hi Delboy
I've exactly the same problem, except that all my keys are now broken so I can't open any locked windows.
After the usual run around with locksmiths who can't help, I may have found the solution at S&D Security Devices in Merrion Street, Dublin. Tel 661 1489
They've located my key type in a catalogue from England. There's no guarantees it's still in stock so fingers crossed while I'm waiting for a reply.
Failing that, they said they could make up a new key if I unscrew the window lock and bring it in to them. Cost at least €40.
I tried contacting the company that installed the windows (for previous owners of the house) and they didn't want to know.