Live At The Marquee is easier to find than Once In A Live Time as far as I'm concerned. In fact, I have only ever seen one copy of Once In A Live Time outside of a JB store.
I don't live in the city or anything, and I had heard about DT, and OIALT was the album they had at the local 'Leading Edge' store. I thought it was good value for a double album, and it looked good, so I got it. LSFNY wasn't out then either...