It looks like Brad is referring to the
" . . . metal trim piece (3-actual pieces per side) that secures the weatherseal to the door frame . . . " and those windlace retainers were used from 1947 through mid-1949.
The late 49 through 55-1st channels are available (they were/are spot-welded to the cab).
As BIG CHEVY 3600 suggested, your best bet is to place a Want Ad in the Swap Meet.
