Sprocket Specialists should have it. I recommend going up 2 or 3 in the rear before going down one in the front. +3 will require an extra link in your chain, but -1 in front will cause premature wear on the plastic blocks that protect your swingarm from your chain. Going more than -1 on the front will also make the chain have to wrap tighter around the front and supposedly causes issues with wear and stretch.
I prefer a 18/45 for general and long trip riding. 17/45 I use for denser traffic and around town riding.