There's very little in the way of 24th decals out there, but with the new kits coming out, this has begun to change. Both Cutting Edge and CAM have released 24th sheets with more to come.
Check out
this page for some reviews of 24th sheets. They're all down toward the bottom, and they're mostly for P-51's but there's one sheet for 109G-6's. I'm guessing that you're building the Airfix 109E?
Anyhoo, as to your specific need, I wouldn't be too awful surprised if someone releases a sheet with swastikas and/or crosses. I think there was an English/European company making such sheets in the past, but the name escapes me and they could be long gone by now. Although, this question has been asked several times before and has received some helpful replies. (Just can't remember what they were!) Maybe one of those who've replied in the past will do so again.
If all else fails, you could paint them.
Fade to Black...