Trevor is right.
Go to a shop where they make stickers for compagny van's ore billboards.
They download a brand logo and cut it out on a plotter in the color and size whitch U want, and it looks the same but costs a lot cheaper than the original.
Now you will bee able to make something that might look original but is a one off design.
I drew the decal on the back with autocad and simpley mailed him the drawing, i jumped on my bike and when I got at his place the plotter was allredy finished.
Everything you can conver to a DXF file is possible to make on a plotter.
The cagiva font on the gas tank is simpley a Windows font, Clarendon Bold-italic-bold.
All the stickers on my bike costed me 25 euro.