Have you looked on Bevals used saddle website? http://www.allthebestusedsaddles.com/ Hmm, well, I just checked, and there is none...I would keep an eye out on there anyways. Middleburg Tack Exchange is a good one, as well as Horseclicks. If you search tons of websites frequently enough, you WILL find one. That's how I found my saddle.
"On the back of a horse I felt whole, complete, connected to that vital place in the center of me...and the chaos within me found balance."
Just keep diligently looking. I found my oldest daughter's on eBay. It took about two weeks of calling various tack shops and checking eBay. I called Middleburg Tack Exchange, Farm House, Judy's, and checked Beval's used saddle web site. Facebook now has a just pony kid's equipment and I have seen 14 inch Pessoa's come up for sale.
Kids grow so fast so they do come up for sale frequently but they sell like hot cakes so act fast. Good luck! They are great saddles. All our pony kids have them except for the one whose pony needed a Butet!