They are out there. I picked up 4 cans (all they had) of light oil ("PL") at a gun show right before Christmas for $2/can. Sorry, but my find isn't for sale.
PL viscosity is about like sewing machine oil. There is also medium oil ("PM") with a consistency like manual transmission oil (75 to 90 weight) at room temperature which was probably for high climatic heat areas and possibly (?) there is a heavy grade ("PH"???) although I've never seen it.
The cans that I have are WWII vintage because the contract info on the can is '44 (PL) or '45 (PM) dated. Presumably they were to fit into a ctg bandoleer along with bore cleaner.
It's good oil to use although more modern lubricants like LSA are probably better for their given use. LSA is difficult to wash off (try getting it off of your hands after oiling a firearm with it. Takes a lot of soap and scrubbing.) So, LSA is better for rainy/damp conditions which was the original Vietnam era purpose. Of course there's the ultra modern stuff like "froglube," tetra-grease, teflon based stuff, etc., etc. but for my money LSA is cheap, available and most importantly proven. The only place I don't use LSA is where lubriplate is called for on M1/M14 type arms. BTW, LSA is actually a "flowable" grease and you need to shake the container well before use.