if their voice mail doesn't work
and / or email doesn't work
find the mailing address from their
website and try to send them
a old fashioned "snail mail" letter
with a return receipt requested.
you will at least know they got your letter that way.

they are a 2 person operation ...
the publisher doesn't come here
and i am not sure if he is at the largeformatphotography.info forum
but i do know he sometimes posts at pnet.
if your snail mail doesn't work maybe post something at pnet ?

good luck !