It depends on the volume, type and quality you want. I buy my 4th class Bucky's directly from the Anatomical Chart Company, during their summer sales. Otherwise I have a lot of Walley's from Walgreens and a bunch of the Pose and Stay from Costco. I have not dealt directly with distributors.
Bucky's for close up detailed scenes:
Wallys - Good for background and where lightweight is needed:
Your best bet is to hope that your local Spirit doesn't sell out of them. Mine had 10 left last year and I left with 4 of them, they were all 50% off. I looked at it as them being BOGO so 4 for 100 bucks. Hopefully I can be the first in the door again this year and buy more.
Mine arrived fairly fast, but it's been sitting at HD for the past few days. They shipped it to the wrong HD and I haven't been by there yet, and I keep forgetting to make a separate trip to go pick it up. I'm hoping it's a decent one, as we need to get several more this year.