The 1954 defroster vents' cover (or window trim - not really a garnish molding but it has been called that) on a 54/55 truck is completely different from window trim used in earlier years, probably in keeping with the change from 2 flat windows to one curved window. The 1954 strip/molding is held down with about 5 screws into the dash and spring-like standoff clips (that are harder to find than the trim-strip/molding).
These parts are not sold in reproduction, so your best bet is to post a Want Ad in the Swap Meet forum.
Tim
