The other guys have already given good references, but I just wanted to add that, after pulling the door on my '51 this weekend to replace the foam rubber weather strip, I had to put the door back together at the end. The two "backing foam washers" (for lack of a better term) that fit over the stems of the window and door handles before replacing the panel/cover that fits over them, might just work, and you can get them from Classic Parts pretty cheap (complete set of 4 of these and 4 backing washers for handles), and they look like the ones that jorb posted. They aren't felt, their more of a closed-cell foam rubber. Just a suggestion if you haven't already ordered, you may want to check that out. The handle stems are about 1/4" - 3/8", so they may be too big for your knob stems, but I just thought I throw this out there.
http://www.classicparts.com/1947-66-Inside-Handle-Gasket-Set/productinfo/18-043/#.WKSOgM_XvX4
