The two you mentioned jumped to mind. 7bit has a group buy type thing going on
over at deskthority, and I think you can get them through the
GH60 Group Buy as well (which I think go through 7bit too... direct may be faster).
Another semi-popular way is to find an old board with cherry switches on ebay for cheap and desolder them. Labor intensive, but in some cases cheaper. (Heck, some people buy new boards and desolder too...)