I bought it at Tracker Marine in Largo, FL but here's the link where you should be able to purchase it on the internet:
http://www.thmarine.com/product.cfm?PRID=168. I heard you can also order these from Overtons (item # 70789)
I got the 2" model for $20 and it fits perfect. It mounts on the existing nut for the livewell pickup so it doesn't require any holes in the hull. I have used it on several trips and it works great, keeping constant water flow to the bait. The seal has also eliminated most/all of the splashing so there is no more spray while up on plane either.
This was a quick, easy, cheap mod and was completely worth it. I would recommend anyone with the same lid set-up to do this.