tclederman asks, "Suggestions on where to look for these parts...."
crenwelge up there has this right, Ebay. This is your best source for vintage parts. Frustration is working Ebay will sometimes take months, even years, to find parts you want. crenwelge also gives very good advice to look at specialty Ebay stores, those which exclusively sell vintage auto parts. Look for "NOS" parts, a safe bet because of being OEM parts.
Ebay can be frustrating, can be time consuming, there is no master parts catalog to use. However, you will eventually find what you need and usually at a decent price. You must be patient and must be willing to work at searching Ebay.
crenwelge and I probably have placed bids against each other.
On detent springs and other odd parts. Often you have to substitute in other brand parts. I am collecting parts to rebuild a 202V Clark trans build back in the Forties. This is in my big 1948 GMC. I want detent springs. I ended up buying Ford brand detent springs for a 205V Clark. I know the detent springs are the same because only differences in a "Ford" brand Clark transmission and a "GM" brand Clark transmission is the size and spline count of the input shaft, ignoring bellhousing bolt patterns.
tclederman, this is when direct experience over decades pays off.
This also pays to ask old farts around here for advice; you are drawing upon their decades of experience. Like others, my old fart experience goes back over three decades, all Chevy trucks with a few Chevy cars tossed in.
I will touch upon detent springs and other parts next post.
This is time consuming. To finds parts elsewhere than Ebay, use the Google search engine. You will NOT find parts by searching for 'transmission detent spring' but will find stores which might have those with 'classic truck parts' and similar terms.
Some Google search terms:
antique truck parts
vintage auto parts
Those two, leave out 'parts' and search again.
classic automotive
classic truck
old car parts
old truck parts
vintage cars
Those type of variations lead to hundreds of web pages.
truck parts vintage OR classic
This leads to lots. Note my "OR" in there. Google will find 'truck parts' then find 'vintage' OR 'classic' for the rest.
Google is your friend, Google will drive you nuts for hours.
Save your good finds in your browser bookmarks. I have a master category labeled 'NAPCO' for my four wheel drive truck. Under this category, 'trans' 'leaf springs' 'transfer case' 'rims' on and on. I subdivide into to specific part types. When I find a decent web page, either just info or a store, I will take a few minutes to add a page into my bookmarks under the right category.
In about a year, you will have hundreds of bookmarked sources. This is well worth the effort.
Much of this is planning ahead. I built myself an attractive but large storage room here on our land. Inside, looks like an auto parts store. I have sections, '48 GMC' - '52 Panel' - '56 NAPCO'- 'Generic' and in those sections I stash all my collected parts, accordingly. I am planning ahead for projects, such as rebuilding an old Clark trans. I collect all my needed parts, from gaskets to gears, before even dropping out the trans. Some parts I will need, some parts I might not need, but I have those.
In the case of an old 235 six cylinder, I actually bought one from a local boy. I collected my parts, rebuild this engine top to bottom, added an alternator and A/C compressor, dual carbs and all that, including those antique 'high lift' intake rocker arms. Took two years to collect parts. Now I have a rebuilt engine on a roll around stand ready to install. When down to a restored rolling frame, I only need to drop in the engine. Same is true for my trans and transfer case; all are ready to go.
This is time consuming, tclederman, but saves frustration. You can still drive your old rust bucket truck while you get together everything you need for restoration. Nothing more aggravating than having your truck sitting in your driveway for a year while you look for parts. Get your parts first, rebuild things first, then take your truck apart. This makes for a smooth and fun restoration project; all you need is ready and waiting.
I even collect doors, fenders and cab parts beforehand. Fix those up, do a custom paint job, wrap 'em with washed soft duck cloth painter's tarps from Home Depot, then continue on with finding parts. You will actually save money by finding bargains before you are ready to use those parts.
tclederman, follow this advice of crenwelge to search Ebay, follow my advice to spend a lot of time searching the web, both 'planning ahead' methods really pay off in the long run.
Billyray