2 Ohm 6x9s

I was wondering if there were any 6x9s that were each 2 Ohms. My 4 channel amp does 70 watts rms per channel at 4 ohms and 140 watts per channel at 2 Ohms. This is a hard detail to search for and so far the only one I have found is Infinity Kappa series 693.7i that retails for around $250. They ebay for less than $150, but I was just wondering if there were others. It's almost a waste to want to run 4 full range speakers across all 4 channels at only half of what the amp is capable of.
I think you are making more of the power issue than you should. Running them at 2 ohms, you will get 3 dB more than at 4 ohms, that's it. Although you can get more power at 2, the amp isn't going to like that more, it will just put up with it and run a little hotter. Hotter is not better. Heat wears things out. Myself, I'd stick with the 4 ohms.

Call me old fashioned,

Yeah, this type of question comes up every once in a while on other forums... but if it was that much 'better', then an awful lot of competitors would be running such a setup and off the top of my head, the only 2 OHM speakers I've ever seen in a truly exceptional sounding install were Orion HCCAs. I think Bose and the like run 2 OHMs sometimes just to play electrical games.
Bridge your amp

What kind of amp ? What car ?
Why do you want rear speakers ? The best systems use only a component set in the front and a sub. They say the rear fill messes with the stereo image and causes comb filtering.
Why do you want 6X9s ? Oval speakers can suffer uneven cone excursion caused distortion. If you can get a 6.5" in your door your golden.
Your 70watt per channel; at times it's getting 140watts now. It's called head room. Some companys market their head room by calling a amp by it's max wattage. Cutting into your headroom to get more power is popular in class D amps running a subwoofer and in sound off dB competitions to meet a certain watt class.
You can probably bridge your amp to make 140 watts X 2 channels. A good quality 6.5 comp set like Infinity Kappa or Orion or even a DIY set could sound way better than four 6X9s.
What kind of amp ? What car ? What else is in the system ? How much can you spend ? How much can you do yourself ?