Pad for a swayback with a short topline?

I recently purchased a little Arab with a very short back with a bit of sway (1.5"). I have been riding him a lot forward and down to bring his back up. The saddle I have is fairly straight so it rests on cantle and tree. I’m shopping for a better fitting saddle but until then, is there a short pad out there to help with the sway that would also not prevent him from raising his top line during exercising? The pad would need to be no more than 28" long. It seems like all the pads out there are made for longer backs. Pony pads aren’t wide enough.

Could you simply shim your current pad in the middle to “fill in” the sway?

try National Bridle Shop or World Champion Horse Equipment. Low backs have become too common in saddlebreds, so they have a decent selection of low back pads.