This is a common question; Where do you get parts?
If the machine is brand new, the dealer has the parts. It is the same as in the auto industry.
If the machine is just a few years old, parts are available through after market suppliers like Tacony, PD Sixty, Brewer, and others. These are wholesaler suppliers, so you will need a business license and set up an account.
There are also retail sources you may find helpful: Temple Sewing And Supply, Inc (254)774-9797, www.SewandQuiltStores.com, www.SewingMachinePartsOnline.com, as well as your local and regional dealers.
Rare parts are available through salvage connections. Most active service centers have salvage machines reserved just for this purpose. Good relationships with other dealers and service centers will pay high dividends with you need that special part.
Keep in mind, if you service 100 machines; only 10 will need parts of any kind. Only a couple will require a major repair.