I was also convinced I had seen these around - but I couldn't find any reference...
I made some myself a few months ago - they aren't that well done (a quick photoshop job) but at least they can be found, here's an A4 pdf:
(clicky linky). There's also a 250/500 Tile in there - and La Porxada, as I was printing this out at the same time.
I would recommend sticking them on to spare 50/100 tiles if you have them