I've seen this also! I can't tell you what prototype it is, or where to get it, but I can speculate! ^__^
http://www.sonic-cult.org/dispart.php?catid=1&amp;gameid=2&amp;subid=3&amp;artid=3
Sonic cult has a screen shot of the messed up title you're probably (probably) referring too.
Since the Aquatic Ruin Zone was still called "Neo Green Hill", we know this was before beta 4, which features an "Aquatic Ruin Zone" title. However, the Simon Wai version does not include a title card for the level (or rather, it still includes the Sonic 1 style card, and the Nick version does not include the level itself)--So we can assume it came before these two protos.
Thus, if the Sonic Team numbered their beta's properly, it can probably be assumed that the Nick version is beta 1, the Simon Wai version is beta 2, and the version you're looking for is beta 3. It's possible the earliest versions we have were numbered differently... But it makes sense to me.

(I apologize for any extreme typos and grammatical errors--I checked this message for them pretty well, but it IS almost 7AM and I haven't slept yet. ^__^" I am going to do so now.)