| Adjust your action down a bit and tap away on your bass. You really don't need a specialized instrument to play touchstyle, especially in the beginning. It's takes a good while to get used to it, and that's one of the reasons you always see them for sale on EBay. Personally I started by playing touch style on my basses, now I actually have a Warrguitar that I love. I've also owned a Chapman Stick in the past. I will warn you it takes some serious work and dedication to make it work well, especially the 2 hand independence.
Happy tapping,
Dirk | 
