Napa still seems to be stocking them at the regional distribution centers so if you need one quick (depending on how far you are from a DC) that may be the way to go. They can't look it up but of you just ask for a 90-417 they should have em. Cost in my area is about $12 each.
After some digging the Napa ones are most likely made by Milton and you can buy a set of 5 direct from them, current price is $41.90. Standard shipping for me was $6.99 so call it $50 with tax to my door. Basically you get the 5th one free vs getting them at Napa.
https://miltonindustries.com/products/miltonr-tr-417-clamp-in-tubeless-tire-valve-box-of-5-471
Other places and prices all over the place. Seeing them as cheap as $10 with free shipping for 4 and has high as $45 for a single one not including shipping. Milton I think is still a good brand so I feel comfortable buying from them vs many of the other options where you don't know what you are gonna get.
I try to keep a set of at least 4 'in stock' and one in the glove box for an on the road emergency.
Feel free to mention a source you have used recently.
Also if you have not had to deal with these before be sure to check and make sure they are clearing the brake caliper after they are installed. If you got rear drums (67-75) no problem but remember to check them when you rotate them to the front. If you don't check them they could rub through and leak.
If they don't clear ideally you have to take them off and use something like a block of wood and a hammer to give them the extra slight contour they need to clear. You can do it in the car if you have to and get the stem in the right position but its easier when they are off. You also want to look at how they stick through the hole in the hubcap, I have had to stick something in the rim hole when I smack em so it stays in the center of the hole. I'm not talking about major re alignment maybe like 1/4".
I just got the order from Milton so not especially fast shipping, took about a week. I forgot to look at the box to see where they came from, if it was Chicago where they appear to be based it must have took a few days to process so Napa may be your best bet if you need them fast and are close to a DC.
They look fine and correct. Not sure when I will get a change to mount the new tires so I won't be able to check the fit for a bit yet.
I replaced mine 9 years ago when the last set of tires was mounted. New rubber is going on, on Monday morning and it appears those will just stay in there. The originals lasted almost 40 years. I kept those and do have a spare complete set of new ones too.