I purchase supplies, strings, and instruments from a number of wholesale vendors as well as directly from overseas manufacturers. BEWARE = the overseas instruments may come with no labels - a shop can make a paper label and claim it is their exclusive brand, when the same instrument is being sold under a different label in another shop.
I have also found some instruments at auctions and flea markets. Sears and other catalogue stores imported millions of instruments from Germany and France from the 1800s into the 20th century. Some of these are ridiculed as "attic strads" - but now they are over 100 years old, the wood is well seasoned, and with some adjusting and repairs, many are very good instruments.
I am a dealer for Bam and Gewa cases. Tonarelli, Bobelock and other cases cases are available through my suppliers.
I am a dealer for CODA Bows. I also get quality carbon fiber bows, pernambuco, and other wooden bows from several sources.
Gatchell Violins has been a trusted partner and always supplies quality instruments and bows. They are the exclusive dealer for Stefan Petrov instruments which have proven winners for some of my customers. I play a Petrov viola and a 1795 Lupot violin.
International Violins has been a strong partner for stringed instruments and luthier supplies for many years. They have also been strong supporters of the Violin Society of America.
Howard Core is a major supplier of stringed instruments. I regularly purchase small items from them and have bought a couple basses in the past.
Metropolitan Music is run by descendants of John Juzek, a famous luthier from early 20th century Czechoslovakia. I recently purchased some hard-to-find tools from them.
The list goes on. Amber, Tong, Angel, Century have all provided good instruments. Pioneer Valley supplies premium hair for bows. And I'm forgetting a couple.