Q: I need a keyboard for my Macintosh SE. Any ideas where I can get one?

Where in the world are you?  Name a large city near you and we might know a recycling company that saves older equipment for resale.  Seattle, WA - Go Seahawks - has a great electronic recycling location.  We have dozens of older keyboards.  User groups will know who held on to spare parts.

Then there is the usual retail outlets.  Ebay has several listed.  Having a rough idea of where you are and what your price range is will help narrow down your choices.