Good luck!
Despite some nice technologies having been out there for a decade or more, transflective screens have never really taken off in the market, except a few niche applications like some smartwatches (but not Apple) and bicycle computers. I remember when the OLPC (one laptop per child) came out with that display from a startup (forget the name) which was poised to make a killing in the laptop market. Never happened. I think it is "form over function:" marketing does not trust customers to value awesome battery life, or sunlight readability, over the general attractiveness of the screen, and because there are always compromises involved, they stick with the "safe" TFT.
I think your best chance is to re-think your enclosure and design it around a transflective screen you can actually buy

Besides the Sharp memory LCD line, Japan Display (JDI) has their own line of low-power, transflective displays. One buzzword to search for is "memory in pixel." Anyway, you can actually buy some of them now at Digikey, although they are fabulously expensive. The panel sizes are pretty much the same as Sharp, too, because it's the same niche markets that are driving both.
I used to believe the free-market dogma that "once consumers demand X, companies will provide it" but now I have seen the light and I realize it is all down to what marketing departments decide to say that consumers want, not what they actually want...