I don't know if a synthetic reining saddle is available. I would think someone would have one, somewhere. My last two saddles have been synthetic. I will never buy leather again. The care required is not only not worth it for me, it's a pain in the behind. Why would I spend all that time on tack when I could be riding?
I am going to soon replace my bridle and will go with that plasticy-nylony type stuff. Really technical language there, I know. It looks like plastic, but its a special kind.
Ah - just looked on the 'net. I think it's called Biothane. My girl is going to get a purple one :)