Sometimes finding that right Swasticka, or maybe its an insignia for a hard to find Squad....
Well sometimes they are available in after market, or you just have to buckle down and make your own decals.
Well believe it or not, another hobbie has developed that mirrors ours somewhat.
Custom Aircraft skins for a Computer game...IL2 Sturmikov, the Aces add on and its newest Pacific fighters.
This program allows users to "paint" thier own aircraft for online play, and some of them are just amazing.
As a result, Websites are popping up all over with templates, color charts, markings and insignias ect.
Now it seems to me, how easy it would be to just print these out on your own decal paper..once scaled properly you have a ready made decal templates out there for free.
As an example check out this site:
http://www.skinnersheaven.com/
These places are popping up all over...just ask Google.