If you just want the conical stopper to cobble something up yourself:
If Springvale isn't too far for 'ya, try KegKing. Otherwise most home brew/wine making supplies places should have them too, if there's one close by to you.
I got a set of silicon stoppers of various sizes for various jobs that may one day need them.
Main one I wanted was to inject air through the Tdi's block to help force out scale/rust build up.
Not cheap, but not horrendously expensive either. average price is something between $2 - $15 for really large 70+mm sized ones(from memory).

