Various cultures and time periods within the SCA period have examples of decorative pottery, something easily mimicked by anyone with access to a pottery painting studio. Of course the originals were created through a different method, such as the beautiful tin glazed polychrome Majolica and Delftware, but not everyone has the opportunity to make these or sometimes they just want to paint something already made and easily available.
It isn't difficult to find many examples of the fancier Majolica plates though simpler, more utilitarian, patterns might prove more difficult to find, likely because many have been lost to time. In the later case, paintings might be your best bet, depending on country and place.
Here are a few examples of some pieces I made on the fly, though I would like to really sit down someday and seriously plan out a project or go full course and make it straight from pottery (something I only have a little experience in)
The one with the coat of arms on it was a first try while the one with the simple knotwork was my last attempt, both of these were done at a pottery painting studio. I included the third on, based on designs from extant examples of tin glazed items, to show the difference on using ceramic paints which does not give results nearly as nice or useful. Someday I would like to make another one with a similar design but using the first method.