I use a rotated 1920x1200 display.
Therefore "1200x1920" resolution

I am finding I have to manually enter random keywords in the google search like "tall / portrait / long / rotated" for my wallpapers but it still, frequently pulls images which are not 10:16 but rather 16:10 :/ for example.

Google does infact support FIIXED resolution images in the google search user interface (at the bottom it says "Exactly..." for image size)
See here
https://www.google.com/search?q=hamuu&hl=en&biw=1272&bih=614&site=imghp&tbm=isch&source=lnt&tbs=isz:ex,iszw:1200,iszh:1920&sa=X&ei=hWOtUf6MMYS1kAXlmYGoDg&ved=0CCsQpwUoBQ#hl=en&site=imghp&tbs=isz:ex%2Ciszw%3A1200%2Ciszh%3A1920&tbm=isch&sa=1&q=XXXREPLACEMEXXX&oq=XXXREPLACEMEXXX&gs_l=img.12...8062.10150.2.11535.15.14.0.0.0.0.206.1183.9j4j1.14.0...0.0...1c.1.15.img.3FXqcqk0AbQ&bav=on.2,or.r_qf.&bvm=bv.47244034,d.dGI&fp=3ad066fcc12d17e3&biw=1272&bih=614

(XXXREPLACEMEXXX) is the search string, the rest is the resolution code

Thoughts?