Hi Reneecase,
Here are some suggestions: Gerber Viper 1.28 gpf elongated. It is considered standard height at 15-1/8" and 14" rough-in. It extends 32" from the rear finished wall to the front edge of the bowl. Model number is WS-21-514. While it's not offered in a dual flush model, it is considered a HET and uses 1.28 gallons per flush. From the research I've done, this averages out to be about the same water usage as a 1.6/1.1 gpf dual flush. The Viper uses standard tank components, for which repair/replacement parts are readily available and very easy to do-it-yourself.
Gerber offers the Ultra Flush 1.1 gpf elongated (model #EF-21-314). It has a bowl height of 14.5" and extends 32-1/4" back-to-front. It is a pressure-assist toilet, utilizing the Sloan Flushmate. They're great when working properly. Repairs are complicated for the average DIY-er and parts are more expensive.
Finally, Gerber's Maxwell Dual-Flush elongated (#DF-21-914) has a bowl height of 14-7/8" and extends into the room 31-5/8". This seems to meet all of your criteria. As with the pressure-assist, repair parts are more expensive for a dual-flush than for a basic gravity flush toilet.
I hope this helps!