I get powdered knotweed (Plum Flower or Nuherb) and cat’s claw from 1st Chinese Herbs. Use LYME in discount code. Good service and shipping.
Woodland Essence has most of the Buhner tinctures, has good service, high quality herbs, and quick but expensive shipping.
Montana Farmacy has good berberine varieties of tinctures and cryptolepis, I believe. Good quality. Shipping is extremely slow by modern standards.
Sage Woman Herbs, Beneficial Botanicals (Buhner’s sole recommendation for lion’s mane), Elk Mountain Herbs, and Mountain Rose Herbs.
Everything I mentioned has been recommended by Buhner.
For simplicity’s sake, look to Woodland Essence for tinctures and 1st Chinese and Mountain Rose for powders, cut herbs, teas.
Here’s the sources page from the old Buhner website. He also mentions sources in his books.
https://buhnerhealinglyme.com/resources/herb-source-list/