Hi -
I have two suggestions. One - try Gold Medal Models. I know they offer a sheet of 1/700 aircraft markings; I'm not sure about 1/350. A good way to get to the Gold Medal website is via <www.steelnavy.com>. If you haven't been to the Steel Navy site yet, you're in for a treat.
Two - if you live within convenient distance of a good hobby shop that caters to aircraft modelers, browse through its assortment of 1/48 and 1/72 decal sheets (by Superscale, etc.) keeping an eye open for American and British aircraft that have kill markings. They frequently take the form of tiny iron crosses and/or swastikas that, if you're lucky, are just the right size. The black and white stencilling for 1/48 and 1/72 aircraft models also is a good source of letters and numbers for 1/350 and 1/700 fuselages and wings.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.