Hi, I'd like to get a ground glass focusing loupe to use with my Crown Graphic. Any recommendations?

Any god quality loupe around 4x will work well. I switched from the low priced Peak plastic loupes to a Horizon GHZ103 for 35mm viewing and it doubles for GG focusing also.
http://www.bhphotovideo.com/c/product/22290-REG/Horizon_GHZ103_8x_Focusing_Loupe.html

An alternative is to use a pair of 2 to 3 power reading glasses for focusing. Take the camera to the store, open the lens on T or Focus setting with aperture wide open and try different power glasses and see which one allows you to see the detail you desire from a comfortable distance.

hey Sierra

it does depend on what kind of shooting you do!
for in side one like
Schneider 4x Camera Lupe
Rodenstock Aspherical 4X Magnfier Lupe
Leica LVFOO Focusing Magnifier
NPC5.5x loupe is what I have one of
all are good but $$ and big
now if you are backpacking then they are not so good
for this some thing smaller & cheaper is better like
AGFA Lupe (Loupe) 8X Magnifier for Slides, Negatives
or a small try Fold Loupe if you drop it & brake it so $25.00
not $150.00 and then one like ebad #330394988736 is good
take with you for size but its $59.99 + shiping
now I do have NPC5.5x loupe but I also have 2 or 3 small
try Fold Loupe that I use most of the time as most of my
shooting is out & about not inside

banjo