The only commercial sign templates I've seen have been simple block letters, due to the limitation of the template needing to be a single, continuous structure. For a script-style "font", I think you'll have to go free-hand, using printed letters glued to the surface as guides.
One of the problems with free-handing is having sufficient surface for the router base to rest upon. An over-sized base, or skis, can help in that regard.
One of the problems with free-handing is having sufficient surface for the router base to rest upon. An over-sized base, or skis, can help in that regard.