If you're willing to do some digging, you could probably find something close at Graphics Fairy or Vintage Printable, and have it printed at a copy shop.

You might comb the stacks at your local library, looking for something you could have enlarged, or go to eBay and search for 'vintage botanical chart'. I have a search setup that brings me anything, on a weekly basis, that's listed as a vintage botanical chart and it's pulled a couple images over the last 6 months that are similar to the one shown above.

You could try contacting Dwell.

Hi,Vintage Printable here (thanks for the link Lemonadefish).
There may be similar ones in our categories black and white (or low color) botanical prints, as well as educational plates
Here are some educational plates that we like, although they have color:
Flower parts, German educational plate
Fungal anatomy
(Images are free to download or print, and scaled to be printable on letter size paper, plus or minus)

There are awesome reproduction educational charts in this shop:
http://www.etsy.com/listing/94661223/vintage-pull-down-educational-chart