We had great good fortune using *Telynau Falcon on our small TB mare to produce a crossbred pony hunter who is being brought along for the show ring by his new owner in Ohio. He can be seen at http://sakurahillfarm.com/horses.php?HOID=38, Sakura Hill Sensei. I believe that Anne Hedge of Whitehedge Farm in TX has had considerable luck with his progeny in the show ring.
Champlain Rainmaker. owned by Nancy Burnett stands in Va. He is not a sec A, however. He is 12.2, passes on a fabulous disposition and is a gorgeous pony. My large pony, Centerfield, is by Max and was the easiest pony ever to start. Centerfield was 2010 USEF Grand Pony HOTY and he is only coming 8 years old.
That is exactly the size of our TB mare used with Sec. A *Telynau Falcon who I think is 11.1 or 2 hh. We chose him because of his fluid movement. Even George Morris has commented on how nice the resulting now 3 yr. old is.
I have 2 very nice moving, well bred, small Sec. B stallions that I invite you to take a look at - both are on my website along with video. Rondo has several outstanding moving babies on the ground now. Another great small pony stallion to look at is definitely Blue Who - www.sugarbrook.com. He is a great mover and super sweet!
I think you have a lot more options than you might think. In addition to the A's, there are many, many Section B stallions that are on the smaller side (12.3ish). Check out the recent VPBA stallion service auction page to see lots of them in one place, all with sizes listed. www.vpba.com That is in no way a complete listing but a good place to see a bunch in one place and compare. See also www.welshpony.org stallion listings for more.
It would be great to hear what you might like to try to improve upon in your mare, then maybe it would be a little easier to steer you in the right direction. I would suggest not only looking on the USEF site, but if you see a stallion you like or a pony in the ring that you like, see if you can find out the breeding and google to see more offspring or contact the SO directly for examples. Good luck to you!