Kelli,
There is plenty on line stores that will ship – just google it. However – are you far away from some bigger city? The best thing is to just go to the store and there you can see and feel it, and there will be no shipping cost!
As far as the size – every but plug will stay in – as long as it is shaped properly – so to have the narrow neck and stopper. But probes will not stay in – they are not made for it. Usually, I would recommend the smallest one to start with and than move to medium one. Even after you get accustomed to the size – small one will be better for prolonged wear (if you are so inclined).
Hope this helps
P.S.
I know you said you looked through the threads, I just thought to mention this one (it was one of more successful ones)
Anal play
also, here is one of my favorite on line stores;
The Blowfish