Your best option right now is to buy one with the interior color you like and have the car wrapped in dark green. Even if Subaru had a dark green in their system on another model they would be reluctant to do a color without testing that the paint would come out right on the bumpers and other panels.
Bmw and Porsche have some special request colors including dark greens that on a Bmw can run between $5,000- $7,500 and add several weeks if not months to the order. Porsche has a rainbow of options that aren’t in the brochure but now charges about $12,000 and the timing at the factory is not easy to predict.
I’m not sure if the Forester’s green is much different from the one offered when i bought my 2015 but on the website it looks like a similar very light green that’s almost gray. I have the blue quartz paint on mine and while i would have loved to be able to get one in dark green it wasn’t possible.
If you want a well done installation with materials that will last a wrap can be $5,000 or more but could be done much quicker than having a paint shop do a complete color change. More commonly done on high end cars where the owners want something unique or to be able to change colors every year or two.
Sadly it’s been awhile since the dark green’s were in fashion with car makers.