Thanks a lot for the information, guys!
I had actually expected this shirt to be a shop-at-home item, since usually stuff like this is sold at the gift shop at the Legoland, but there was no Legoland in the US in 1985.
I don't recall this shirt (or any theme based shirt whatsoever) to be seen in any German catalogue. The only shirt that actually made it in the regular catalogue of (I think) 1982 is the following:http://www.brickshelf.com/cgi-bin/gallery.cgi?i=592144
( A friend of mine actually fits into it. Tight.)
(But that has nothing to do with Lego Castle, so I'll stop it here.)
This is just the sort of nonsense up with which I will not put.