just go to napa or oreillely.
O'Reilly are only semi idiots
When hunting for school bus parts, remember it is a truck, if it is a dog nose it really is a truck from the firewall forward. Instead of say a dump body or cargo box, it has a long frame with seats. RE and FE buses are still trucks. You have to go to places that sell truck parts. The chain store parts stores as a general, rule employ people who don't really know much about cars and nothing about trucks. If they can't look it up by make, year, and model in a computer, it doesn't exist. NAPA is a chain, but they have truck parts and are usually, at least in my area knowledgeable about trucks. Old local
autoparts stores, even though they may be some sort of buying/marketing group now will probably know trucks. At least around here the counter people either grew up in the business or were mechanics. Most of them know what the part is and at least what it is off of and what it does, when you lay it on the counter. As a general rule the web isn't a good place to look for truck parts. Heavy and medium duty trucks are still basically built one by one. They come down an assembly line, but each one has a build sheet telling what parts and extras are to be installed.
You need to find out what kind of truck you have, if you have a dog nose it's easy, show us some pictures. There should be tags all over the place telling you what things are. On a truck, EVERY
major component has an information tag, this includes axle,air compressors,etc. Find them all and make notes, I take pictures of them all, I then have the pictures on my phone. I also print them all and put them in my "build" book. Your camera/phone has the capability to take good clean close-up pictures. If you don't know how, LEARN
. It's even possible to get a picture of a tag that you can't actually see, if you can get a camera pointed at it. Thomas, at least when I contacted them were quite helpful, you need the VIN# to do anything having to do with a truck.
Your original question was answered by people who know what they are talking about