I am a member of the Society for Creative Anachronism (henceforth referred to as the SCA). We re-create the middle ages with all the uncomfortable bits (like not bathing and no indoor plumbing) left out. It is not a Ren Faire, or a Fantasy Faire, rather we strive to be as accurate as possible for our individual persona’s time period. It is sort of like the Civil War reenactor folks, we just cover a much broader time period and geographic area. You can find more information, local groups and links at the main Society page.
I am involved in the Equestrian part of the SCA in our Kingdom. It is nearly impossible to find modern tack that is period-looking and most folks make their own. However, I have found one place, that if you are willing to fork over the cash, has some REALLY cool pseudo-period tack. It is the Baroque Horse Store. They mainly specialize in imported folk tack from central Europe. They also carry Spanish and Portuguese tack and saddles. My favorite is the Hungarian Heritage Bridle. There is also a matching breastcollar. They are really neat, but very pricey. I can't show pictures, as they are protected on their site. I did find a photo of a similar one.
I also like the Portuguese presentation sets like these.
So, if you have some time to kill, check out their site, they have some very unique things. If you see something you can’t live without, try Googling it, you might can find it at a more reasonable price. I know a couple of eBay sellers offer Spanish tack at a very reasonable price, though I can't vouch for the quality.