JRam:
Nice score on the drill press. Here's some info on the parts you're looking for:
41-45 is the chrome spindle guard. Not unusual to see them missing and somewhat rare to find in the wild. Every now and then you'll see one on eBay. They historically go for around $65-$75 in varying conditions.
60-29, the belt and motor pulley are easy to find. There are always pulleys on eBay in the $15-35 range. You can buy them brand new from Electric Motor Warehouse for $25 plus shipping via Amazon, maybe eBay. They're 1/2" bore pulleys but they include a bushing for 3/8" motor shafts. I've bought three and they're perfect. Belts are standard auto parts house items.
BDI-61 is a standard-issue Jacobs chuck key. Our local Ace Hardware has those on the shelf or you can source them from Amazon or direct from Jacobs. Ditto with the chuck removal wedges, 51-57. Those are #6 wedges assuming your DP has a Jacobs 33 taper chuck as installed at the factory.
50-21A is the quill return (balance) spring. You can find those on eBay or Amazon. Should run you around $15. A local clock repair shop might be able to help you with one of those as well.
Finally, 51-55 is the column tube cap. Unless you're looking for a factory original, Ace Hardware has those. I think they're call plugs or something like that. Probably in the plumbing section since they're trim pieces to close up holes not used in sinks (as in sprayers and soap dispensers) and the like. I paid around $3 for one, tweaked the "fingers" that hold it in place and dropped it right in the column for a nice, snug fit. Be sure to measure the ID of your column before you go shopping.
By the way, you might go out to the Vintage Machinery Web site and post an ad for that spindle guard. I got real lucky and found a guy who was parting out the same Atlas-badged drill press and got the correct factory parts to replace the missing/abused parts for mine.
I'm no expert on this subject but have restored three old DP's, one of them a pre-WWII Atlas/Dunlap that was a basket case, and will be glad to pass along anything that might be of help. Best of luck with your project. Those are some nice DP's and will give you many years of service.