The easiest would be to go off to a local printer and have them print a rosette onto clear vinyl and then just apply it to the sound hole. Maybe a forum member could point you in the right direction there.
The second option is to buy the real thing like this.
http://www.stewmac.com/shop/Bindings,_trim/Rosettes/Guitar_Soundhole_Rosette.html?actn=100101&xst=3&xsr=14295 The down side with this route is that you’ll have to route an inlay channel around the sound hole and then bond the rosette into that. The rosette will have to be sealed, so that means that the guitar will need to be refinished, costly but the most effective way IMO.
