I am also a fan of the Deathadder shape, and have been using it for a long time.
The mouse that is most similar to the Deathadder in terms of shape, but also very similar in terms of performance (sensor without acceleration or prediction, a high enough tracking speed, and several DPI settings comparable to those of the 3.5G) is the Zowie EC1. To give an idea of how similar the two are, here are a few pictures
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(the one on the far right on the picture above is the EC2, which is similar in shape but slightly smaller)
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I have used many of the optical mice with a similar shape and size to the Deathadder , and I felt the EC1 was closest. The most notable differnce between them are that the Deathadder is a little more steep on the right-side, fans out more toward to front and has a scroll-wheel that is placed not as far forward. Also side-button placement is slightly higher on the EC1. In general I can recommend the Zowie mice, I have had great experiences with them and they seem to be generally well regarded.
Getting another 3.5G (if you like the mouse) is not the worst option, since they can be gotten pretty cheap now ($30-$40) as they are mostly treated as excess stock. If you can not find a place to buy them, check out Takasta's ebay store. He even sells special versions that have another coating (personally I am big fan of deathadders with glossy coating, but it is not for everyone)