Not apart from the supplier mentioned, but on the assumption that "they" don't make there own and assuming "they" are not pulling a fast one "they" must have a supplier. Probably Streamselect or BP Nutrition or one of the other big commercial suppliers.
You could always over spray "standard" pellets with betaine youself. Don't forget betaine is soluble so you can make up a solution and then spray your own pellets before you use them. You can also add all sorts of other solubles to the spray but watch out for overload if you are using lots of pellets.
Cy.