Thanks for your always inspiring work, Kieran. I've learned a lot of terrain making techniques from you. I'd love to see more of your planes.
Boggler:
You can try I-94 Enterprises. Dave (the owner/artist) has many number decal sheets in red, yellow, black and white. He has USAAF and USN lettering, as well as standard sans-serif fonts, and German tank numbers with surrounds that you can use for Luftwaffe planes:
i-94enterprises.com/decals_3.htm
His LB-100, LW-100, and LR-100 sheets would be good for squarish squadriglie numbers.
I also got a few letters and numbers decals from Microscale. Much more expensive at $6.50, but they will never run out. They cover a few different fonts that Dave doesn't have, if you are that picky about specific font styles!
link
The ones marked "11/64th, 1/8th, 3/32nd, 1/16th, 3/64th" have the most variety of sizes. "Railroad Gothic" Nos. 90101, 90102, and 90105 (white, black, & red) are a font like Arial or Helvetica that is more suited for rounder squadriglie numbers.
Glad to and hope to be of help!
Rolando