If you are looking for Victorian Corset busks, there are plenty of sellers that sell them on ebay for a reasonable price. For actual late 16th C into the 17th C pair of bodies busks - i think most people end up carving them themselves.
Personally, for my Victorian and Edwardian corsets I wear to re-enactments, I loathe busks. Those hooks and I do not get along. I've gone to another very period front closure- buttons! Flat, round buttons were very often used in Victorian and Edwardian corsetry. If you decide for an alternative to busks, buttons may be another way to go! If you like, I have several photos of extant corsets with buttons (some are from my site, some aren't. I keep them on file for documentation purposes)