Wanted - 11 tooth Shimano cog for 10 speed

[Flying Dodo]

I usually mix-and-match cassettes as I've found an 11 speed cog seems to give me just the right cadence for going flat out, rather than a 12. However, it means I've ended up without the final cog for a 10 speed 105 cassette I want to put on the commuter bike.

So has anyone got an unwanted 11 tooth cog lying around? Part worn will be fine.

Thanks.