http://www.tippmann.com/ETriggerElectronicUpgradeKit.aspx
I bought it recently thinking I was going to use it, but decided not to. Still in the packaging, never opened. They retail for $100, I will sell for $90
and will including shipping (flat rate USPS) to the US.My originally bought it for the "auto response" mode (gives you one shot per pull and release of the trigger (so two shots per normal trigger function)), and while a lot of parks have a rule against full-auto, the response mode usually gets you around that since you still have to pull the trigger every time.
I'll be going a different route in paintball, and no longer have the need for this.
Comes with 5 total modes: semi-auto, auto-response, full-auto, 3-shot burst, turbo.