In photographer Robert Frank's book "London/Wales" there is a
photograph of a musician carring a bass guitar (the kind like a big
cello) up a flight of stairs at night. Is there any way that I can buy
a print of this picture?

Hello,
The link below takes you to a page where you can see the photo you're looking for:
http://www.new-york-art.com/mus-Corcoran-Robert.htm
I may tell you later where you can buy a print.
luntes