The Grosset & Dunlap Omnibus

Around 1971, G&D produced an omnibus of the first three books in not only The Bobbsey Twins series, but also Nancy Drew and The Hardy Boys.  They are not terribly difficult to find, although there are not many our there--for all 3 series.  I'm guessing collectors just aren't that interested in the these omnibuses.  I think the Bobbsey Twins omnibus is more difficult to find than the others, but once again--this doesn't seem to translate into conductibility. 

These scans are courtesy of Jim McNamara.