Are you wanting only paper or willing to use plastic hulls.

If plastics are OK, get them from a trap club.

Around here, very few trap shooters load their own ammo any more due to the cost of shot and powder - it is not cost effective nowadays. They pretty much all shoot factory trap loads and the club now has to pay to have the empties hauled away or do it themselves. Since many are normal trap shooters, they are 'above' such meaninless 'work'. I get all I need or the brand I want (AA), once fired and free. If that isn't a possibility for you, any gun shop that sells components, can get empty hulls for you. You merely need to shorten them yourself.