The latch mechanism is sold just about every major vendor:
http://www.truckandcarshop.com/trucks47_59/t47_074.html
For the catch bracket Have you checked the classified ads on the forum?
someone has a 58 GMC paring out
Other :craigslist/ebay may be the best bet find someone selling a hood and see if they will part with that piece
There is a guy up here in Ft.Worth on craigslist has a vast collection of TF truck parts Lynn,real nice guy, he may ship it to you,cant hurt to ask, here is a link to one of his ads:
6cxs7-4584407856@sale.craigslist.org