You haven't looked in the right places. Speakman has some eco friendly shower heads.
http://www.speakmancompany.com/products/list/Shower/LEED+Standard+Eco+Friendly+Showerheads
I have no experience with the Speakman shower heads, but I may try one out one of these days. They have some adjustment, but I do not know of they can be rain like.
Waterpik has their "EcoFlow" series.
http://www.waterpikecoflow.com/ I do have 2 of the three models that they have in hand, the 3 mode Ecoflow 1.5 and the 5 mode Ecoflow 2.0. Both work as advertised with respect to water flow, but the 2.0 disappointed in water consumption compared to two other shower heads that I have. It used the same amount or slightly more water as as the EcoFlow 2.0. That means that
this waterpik NSC-623 used more water than this
waterpik shower massage and the Interbath Rainmaker that I have. It seems that some 2.5 gpm shower heads have about the same flow rate as the 2.0 gpm shower heads.
As for the 3 mode EcoFlow 1.5, it definitely has a reduced flow and it is noticeable compared to the other shower heads that I have. Due to the reduced flow it does have a rain like flow for the normal mode. I think the massage mode produces a bit to much splash which can end up outside of the shower unless you are fairly short.
Oxygenics has some low flow shower heads, but I avoid any type of shower head that aerates because they can increase the hot water draw due to the cooling effect of the aeration and they put too much moisture into the air. i had something similar and it put too much moisture in the air and then I had mold problems. Besides they can be quite forceful, which is not rain like.
When looking to see if there was any info on the Interbath shower head I came across a few Australian sites with information on low flow shower heads. You might have a few more choices if you were in Australia or ordered from an Australian company.
If you want to check out the 3 mode EcoFlow 1.5, it should be available at Target and Ace Hardware.