Congrats on finishing your Firefly !! As far as "decals"...that depends on what your Markings may be. One of our resident Detailing Gurus, the incomparable Swathdiver, has posted an excellent tutorial on making your own decals somewhere in here.

If you want to go more or less "ready Made", a Company called MICROSCALE makes water-slide decals "sheets" in a variety of colours if you want to cut out your own "unit symbols".

Tank "Designations/Serial Numbers" may be avilable as dry transfers from LETRASET or CDS (latter also available at the RR shop). MICROSCALE may also make the water-slide type letters/numbers in appropriate sizes ...ie, G-scale (1:22.5). Any well -stocked Model RR shop should be able to help.

Another place to look - "Aftermarket" Decals for Model Airplanes, either static or R/C Types. The latter are die-cut from thin Vinyl/Mylar and take Testors Dullcoat (bottle or rattlecan) very readily. I've used all of these products at one time or other on my own tanks....

Worth a try, eh? More Pictures please!!!