As an ex-golf professional(retired), now screen printer & embroiderer, I can tell you factualy the absolute place to go is the PGA Show in
Orlando, FL all of the big name supplier, manafacturers, are there, make friends and place an order. Be aware however that the biggies will sell only to green-grass accounts(must have a golf course under your feet). They don't want their $59.00 retail shirt being sold somewhere for $29.95.
Higher end golf apparel including sweatshirts 
