I've been involved in clubs that sell ammo. Its doable to licence a few members to sell the ammo, and if you can get large discounts it may benefit members.
It was also argued its a PITA for the few members (read volunteers) that have less shooting time as they get interrupted to sell ammo, there is the requirement to track the inventory in and out as well as tax issues, accounting etc (read more volunteer time needed) and in the end if you want to go shooting, pack your gun and your ammo and take it to the club.