Thanks for the post.
Here in the States one of the most reliable people/haulers is John Freeman.
This guy is known from coast to coast and it's all he does. He recently transported my Ariston from Oklahoma to CA and back. His rates are very reasonable and he will work with you to put together a deal.
Even better, he owns an Aquarama and knows Riva boats very well.
Here is his contact information.
Tell him I said hello.
If that does not work I have a couple of back up's as well