I found these guys through Ebay. They sell their products at a reasonable price and deliver quickly and free. My last consignment I bought from them directly and will definitely buy from them again.
Description
Set of 8 adaptors for converting impact drive sizes.
1/2" F x 3/4" M - 1 piece
1/2" F x 3/8" M - 1 piece
3/8" F x 1/2" M - 2 pieces
3/8" F x 1/4" M - 2 pieces
1/4" F x 3/8" M - 2 pieces
Made from chromium-vanadium steel for strength and durability and helps resist abrasion, oxidation, and corrosion
Black phosphate finish
Supplied on metal storage rail