I can’t speak to wholesale sources, but in WI there are at least a couple Mennonite bulk groceries that sell larger quantities of dried herb & spices. Also lots of other bulk products – I’m not sure how large a volume they’ll sell at a time, but could be worth asking if you are near one (I don’t know if they do mail order)
I buy what I don’t grow myself from Mountain Rose Herbs when I can. They do offer a bulk discount, although I wouldn’t consider it necessarily ‘wholesale’ pricing. I have been pleased with their quality and ethical practices. Unfortunately S/H can be a bear if you are on the east coast like me, but as long as I buy a decent quantity at the same time it’s not too painful.