Websearching for the above finds me arms for the Kingdom of Spain, various municipalities and provinces, and some historical entities. That and links to a lot of English, French, and some German sites.
Anyone have a good site for Spanish?
I am painting up a few Irregular and Minifig Spanish knights and would like to get the shields to resemble historical arms.
Broadly speaking, the keywords you are looking for are "heráldica", "escudos de armas" and "armorial".
Take into account however that heraldry developed a bit later in Spain than in other parts of Europe; there are few preserved contemporary documents from the 13th century, and most of those early documents are "blazoned" rather than "figured", i.e. they contain the technical description of the arms in text rather than illustrations. There are, however, some later collections - from the 14th century onwards, but especially from 1450-1550 - which contain the arms of essentially the same noble houses, and there have been some reconstructions based on the descriptions. You can get reasonable patterns by using the older, simpler arms in those later catalogues, or by depicting isolated elements of later composite arms.
If you don't want to be too specific and just want to get the gist of how did Iberian arms look like, I can give you some representative images.