Now at a push, you can add a little bit of WD40 to the ribbon to reactive it. I've done this with a couple and it's worked and whilst it was better than nothing, it's not ideal and at some point you're going to need replacements.
In the UK, you can get them here:
In Germany, there are several suppliers.
Do a search for "10600003204" and Drucker and you should find several places that have them in stock.