I am looking at one now that is surplus to my needs. I may have a screw too; I'll have a look later. I can probly get it in the post monday? Any good?
Cover postage and I'll be fine with that- it didn't cost me anything.
If none of those suggestions work, start at Alf's eminently useful list of second hand tool dealers, and phone them up. (You are after the sort of bits that aren't generally worth photographing and listing, but do accumulate where old tools are sold.)