A lot of the shows have links to merchandise on their official page.
The Playbill Store is good as a central place, but they are also buying wholesale from the productions themselves, so their stock may be somewhat more limited and may be marked up slightly higher than buying from the shows' sites directly.
Creative Goods does maintain a website at broadwaymerchandiseshop.com, and Marquee Merchandise runs the Broadway Store site (www.broadwaystore.com) so their Broadway shows all pop up there if they don't have a show specific site (Marquee also runs the Roundabout and LCT merch sites).
Edited to add: I completely forgot that Max Merchandise now runs the Playbill Store, so any of their shows would most likely have the full merchandise line up on that site.
Updated On: 8/16/18 at 06:07 PM