Jane_ the only place I know of is
STM (914-273-5500/ fax 914-273-2065) They are located in Armonk,
NY, and have a brochure detailing size, costs etc., which they will
send upon request. They are very expensive, but the granules are
well made and even in size.
Sometimes there are people on Orchid who have extra granules, or who
want to split an order.
Hope this helps