Does anyone know how to convert 9vdc power to 12v dc power?

Does anyone know how to convert 9vdc power to 12v dc power? ive looked all over the internet and nobody seems to have any schematics for anything like it. It needs to be about one or two square inches. Its for a pellet rifle with a built in air compressor so i can travel through the woods and not have to worry about going back to the truck and airing it up. please email me at mongoose_08@yahoo.com thanks