Try this company:
Card Protection Plan Limited, Holgate Park, York, YO26 4GA.
www.cpp.co.uk
Telephone: 0870 120 1251
I have a credit card protection policy with CPP, and, apart from providing cover for my cards, they also gave me key tags (metal) that have a freepost address stamped on them. CPP know whose keys they are by the policy number that is also stamped on the tag, but the finder of the keys does not know my address. I don't know if you have to take out a card policy, and you get the tags free, or if you can just get the tags. Best of luck.