http://www.andymark.com/product-p/am-0244.htm
As per the above, I would like to purchase a stock length of 3/8" schedule 80 PVC pipe so we can make spacers to custom lengths. Again, this is a 3/8" Inside Diameter. (Outside Diameter at AndyMark is 0.68")
Does anyone know a supplier, or have worked with one? Google searches seem promising but there’s a lot of pipe-based technical lingo that confounds me.
Whenever I need anything for an engineering project, I always check McMaster first. They have pretty much everything under the sun.
That is amazing, thanks Arthur! Do you happen to know how they ship something that size?
Anything from McMaster that’s long and narrow will ship in rigid cardboard tubes between 2-4" in diameter and 4’-10’ in length depending on the size and quantity ordered.
Call a local plumbing supply house, they probably stock it.
If the yellow pages don’t yield one, call a plumber in town and ask for the name of a plumbing supply house.
Pipe size does not have any logical relationship to actual dimensions. 
3/8 schd 80 is commonly available at Home Depot, Lowes, & hardware stores. Typically as nipples rather than long sections of pipe.
Schd 80 refers to wall thickness. Be careful to not get the more common Schd 40. 3/8 pipe is .675" OD, schd 80 has a .423" ID