Vallejo do sell a 72 Military paint set in various online hobby sites. You just got to find who offers itthe best price. Vallejo also have various paint sets for different subjects. ie: WW2 Allied, WW2 German Luftwaffe, WW2 USN, etc...
I buy paint I need for the subject(s) I'm working on or in my stash. It's nice to have it on hand ahead of time. Once in awhile I might pick up a color I never heard of or oddball brand paint just to have it. I have Gunze Sangyo's White Green (haven't figured out what's the color I can use for), and Steel Red as well as a couple of Russian brand paints called Akah. I have both A-14 Steel Grey (used forinterior metal & wood surfaces {wheel wells, wing flaps, engine mounts/frameworks, aircraft engines, and wheel discs of aircrafts} and Old Tires Dark Grey which I use for tires on most aircrafts.
It doesn't hurt to pick up an unusual color for you'll never know what it can be used for.