Unfortunately I can't tell you much about side saddles, they're pretty rare really, it may take some serious looking to find what you want. I did a quick search though, there are a few consignments sites that might have what you're looking for. Some have been restored and are pretty pricey, but several look like they just need a good cleaning. Hope this helps:) Side Saddles - Sales, Consignments, Custom Orders
You might be able to find something good on Ebay as well.
Try Elan sidesaddles, Hundred Oaks Inc, about $900 to $800 for a new english saddle they help you with the size. They are only good for the basic learning, you'll probably have to invest in a more expensive older name to go farther. You can get western there to I think, there is Circle R to but you can expect $4000 to $ 10000 for one of those, but I don't know if they are in the US or not. I got a second hand western sidesaddle for $800, she was trying to get rid of everything.