Marc Morin purchased his belts from Vintage Audio For You Too in Bryan, TX. He sells them on the bay as well, $12.45 on the bay for a single belt, free standard shipping and add the tax
I have a few here that are available, $15 plus shipping. We add include some talc and a nitrile glove
Marc worked with AKer StuartB to learn his XA & XB upgrade techniques, we use the same source