I didn't know you could type the bucket name into the folder text box. That solves my problem!
My connection tests fine, but it won't find the bucket. it also won't find the bucket when I try to get to it in a C# program ( a process I was trying to avoid for a one-time download) so it looks like a rights issue on their side.

Unfortunately I can't talk directly to their IT staff; I have to go through my contact who goes through their contact.... (sigh).

Thanks again for the tip!
Lou