It may be easier to take-up a squadron number plate from a squadron that previous did a similar role than get a shiny new one. 5001 (Airfield Support) Squadron did this.
Previously they were known MESF (I think) and because their main role is airfield support (setting up Rubb hangers and PAAG) they took up one of the old 5xxx series squadron numbers that were assigned to RAF airfield construction squadrons.
You'll probably find no matter how unusual your units activities there is a historic equivalent with their own numberplate laid up somewhere.