Here is a list of suppliers and resources that I have found helpful and reliable.

Tonewoods

Steve Keys at Keystone Tonewood is helpful and approachable, and definitely knows his stuff. He selects wood from the original timber suppliers and cuts, grades and stores it in climate controlled conditions in his workshop in Rochford, Essex. I have used him exclusively for back and sides sets (rosewood and figured walnut), for spruce soundboards, 'cedar' (i.e. Cedrela Odorata) neck blanks, and ebony fretboards. All excellent quality and perfectly quarter-sawn.

All his (Indian) rosewood is pre-CITES, and I understand that when it runs out he won't be stocking rosewood any more. His stock appears to be vast, however, and he doesn't expect to run out for a long time. And, of course, as it's pre-CITES it's all pretty old.

Check out his website at https://www.guitartonewoods4luthiers.co.uk.