Want to Buy Minus blue (Waretten #12 or equivalent) gel or polyester filter (not glass)

That should have said Wratten#12 or equivalent, of course.

I am prototyping an optical device in a non-photographic context, and need one or two of these. So if you have one of these you aren't likely to use again, please let me make good use of it. I am in the UK, but these are easy to post, so anywhere in the world.

I'd also like to try the tricolor filters, but apreciate these are less common.

Thanks.