Any sign maker with a vinyl plotter can cut them for you, I've done my own and they have lasted the full season and they don't look like falling off. You can get any font type you want as the software uses any normal text font and converts it to a vector graphic for the plotter to use, If you want something special expect to pay more as they will need to spend time to design it.
The ones I did for myself are a three layer design, similar to the JP type and can be read from both sides of the sail, It took about 20 minutes for me to make and apply them and about $10 in material...but you'll be looking at about $25-$30 for a sign maker to do them for you. Mine are cosmetic as I don't intend to enter any events, but make sure you check out the rules for sail numbers if you do as there are some requirements.

cheers.