I just purchased an M. Toulouse Jennine in an 18" with a long flap.
It's the roomiest flap I've ever put my absurdly long femurs on. (In fact, if I had it to do all over again, I would probably get a 17.5") Both the front and rear blocks are moveable. I believe Toulouse also has some models with larger blocks, and they have several models with a long flap available. I would suggest calling Classic Saddlery and talking with them. They will give you a week trial period on a saddle, and they were really helpful in steering me to the right model.
Does anyone know about a Kent and Masters s series jump saddle? They look REALLY nice and I love the idea of the adjustable billets, gullets, and stirrup bar. Plus it comes in black! I love black saddles....but that's not really important ;)
I have the Genesis system in my Toulouse. I like that they added a locking mechanism so that you don't have to worry about it spreading wider as you ride (which used to be a problem with the Rembrandts when their Wellup system aged).