I'd been looking on Amazon for a handlebar mount for a long time and every time I order it, it goes out of stock. Then I saw this article (http://www.instructables.com/id/EAKFO4VEB6EP306G7G/) and was inspired. I decided to use a different approach though, because I don't want to modify my gps unit in any way.
This is an almost entirely made from scratch solution that didn't cost me anything to make. Of course it helps if you already have some tools. :)
Step 1: parts list
some sturdy scrap metal. Mine is a piece of brass about 1mm thick, though you could use probably any kind of sheet metal.
a cheap handlebar mounted reflector or similar thing. Mine came with my bike as a freebie to mark the place where your headlight should go.
two machine screws with matching hex nuts or the like.
a means for cutting metal, I used a jeweler's hand saw
pliers or metal bending tool