Food for thought...
Per the Master Parts listing, these where used on a wide selection of trucks from '37-57 (depended on model). Maybe another 'Bolter may have something saved/stashed or accessible from a parts truck?
Maybe put an ad up in the "Swap Meet - Truck Parts Wanted" forum?
If I find any other possible sources, will pass on.
EDIT: Here is another source I found:
There site states a minimum flat shipping rate of $9.95 based on orders $0-24.99. Your costs depend on how many you need (these are a bit more than the other source noted).