does anybody know where you can buy a cover(cowl) for a 15 hp motor that says it is a 9.9?

Do you have the cover for the 15?  If so, a new coat of paint, and some 9.9 stickers would do the trick.  There are quite a few ebay stores that sell just outboard motor stickers.  Never hurts to repaint a cowl neither.  

Or, just get a cover for a 9.9.  The engine is the same size, so a 9.9 cover will fit just fine.  You can find covers on ebay from time to time, as well as any boat junkyard, or if you can find a shot motor, take the cowl, and UPS the rest of the motor to me.

just buy 9.9 stickers. that is what I did. bought them from the dealer I bought the motor from