I've never seen a flag with a space.
https://www.vanguardmil.com/products/civil-air-patrol-guidon-flag shows it with a space and if you google "Civil Air Patrol Guidon" you will see some with spaces, without spaces, and even a few dashes.
Examples:
VA 124
VA124
VA-124
If you go by CAPR 900-2 (which you should, instead of what may be shown on Vanguard's website), the correct answer is no space and no dash "VA124"