I get 99.975% of my old truck parts from local guys.. Advance Auto Parts can order just about anything you need, at a low price.
When my '46 2 ton needed a pressure plate and clutch disk, Chev of the 40's wanted $80 for the pressure plate alone, with a $50 core charge, and another $48 for the clutch disc, with a $40 core on the disc, plus charge me for shipping.
Auto Zone sells the pressure plate for $59, and the clutch disc for $33.. you pay no shipping, and the parts are delivered to the store the next day.
Theres a $6 core charge on the disc, and a $12 core charge on the pressure plate, but if you bring the old parts in when you pick up the new parts, there isn't any core charge at all.
Che of the 40's sells a generator for $95 plus $75 core charge.. my local guy will rebuild my old generator for $85, and no core to fool with or pay to ship back.
Chev of the 40's sells a rebuilt foot stomp starter for $116 with a $50 core charge. Adance Auto Parts sells the same starter for $111 with a $30 core charge.. and again, bring your old starter in when you pick up the new one and there's no core charge.. and no shipping to pay.
Those are just three examples, but in most cases, the only thing I find the catalog places to be good for is repop trim parts, door handles, that sort of thing.. which I don't like to use.
I can buy original good condition trim parts off eBay, or thru places like the Swap Meet section of the Stovebolt much cheaper than the catalogs sell the repop stuff for.