Here's the JG27 Unit Crest you're looking for:

Print that image onto a regular piece of paper with a color printer, spray the back with 3M77 (or similar) and stick it on. Be sure to fuel proof it too.

Major Decals has 1/12th scale German crosses available here:
http://www.hobbypeople.net/mfr/majdec01.asp
Sheet "865703 7003PS Major Decal 1/12 German (WWII) Press Sens" is what you need for $8.75.

The '14' can be cut from Yellow trim sheet or sign vinyl.

Japanese Hinomaru can be cut from Red trim sheet or sign vinyl. If you want the style with the white surround, cut White discs that are a little bigger than the red ones and laminate them.

HTH,
D