Hi,
I bought 72 markers from this seller on ebay:
http://search.ebay.com/_W0QQsassZlotsofjoblotsQQhtZ-1
It was NOT the 72 marker set - they are individual and do not come with the case, but he lists the ones you get (or are likely to get) and I think that I got 68 of the 72 he listed. The other 4 were different from what he listed, but they were all different, so I didn't care that much. I already had the 24 set, so I ended up with only about 10 repeats. Right now, he has 72 markers and 48 pencils listed for $79.99, which I think is a great deal! The only thing is, he ships from Canada, so it will take a little longer to get here, but I couldn't be more pleased.
The other individual markers I plan to get here:
http://www.markersupply.com/prma.html
They don't have all the colors, but they have enough! It is one of the few places that seem to offer reasonable shipping on these. I haven't ordered from them yet, but I hope to soon, so I can't speak to their customer service or shipping speed.
Hope that helps a little!
Connie