its very easy to rig up one of your own. im not exactly sure what av10 exhaust mounts are like, but if theyre like av7 (probably pretty close?), you can just stick a looong bolt through the mounting holes, and snug it on with some nuts and washers. this will give you a very long "lever" to put your foot on to keep the engine in its low-gear position.
i rigged this up on my engine and it took all of 2 minutes... but i havent run the bike yet so i dont actually know how effective it will be. pretty simple device though, i cant see how it would fail.
if youre using the stock pipe, though, these mounting holes will probably already be in use so you could drill new ones.