As mentioned above, Mark Comstock for seed grown Japanese Black Pine
The two finest grafters, producing stock where the scion is grafted right into the root zone of the understock, there are only two sources I know of. Brent Walston at Evergreen Garden Works and David DeWire at Wabi Sabi. Both gentlemen produce excellent, low grafted select cultivars of Japanese white pines, Japanese black pines, and in David's case a wide range of other pines. Ask David about Jack Pines grafted for bonsai. These would be my go to sources. With Brent, his listings are often on the web as sold out. Email or call him, get on the waiting lists. Once you are on the waiting list he will contact you about each as they become available. Also with Brent, if it is now, say January, and he has a tree listed as available in June, with a price. Pay for the tree in January to be shipped in June, and you will get your tree. If you wait until June to order, it may very well be sold out.
Wabi Sabi Bonsai is a premier Pacific NW bonsai and dwarf conifer nursery enjoying 35 years in business with full hands-on experience in propagating, growing and training high quality, rare plant material for the creation of exceptional outdoor bonsai and outstanding landscapes.
www.wabisabibonsai.com
'
Julian Adams has 'Zuisho' JWP, his availability limited, so a call or email is needed rather than just clicking buy it now.