I contacted Chris Matgouranis, the student who generated the "5,000 janitors with PhDs" figure cited in Richard Vedder's Chronicle piece. He helpfully pointed me to 2 Bureau of Labor Statistics sources.

The first, here, gives the distribution of educational attainment in various professions. The second, here, gives the number of people in each profession.

Alas, the BLS has chosen not to provide exactly the same categories for each, so I'll have to write a script to merge the two.

For now, though, I've put both sets of data into a Google spreadsheet here.

Overall, 3.8% of the over 25 workforce has PhDs. If you sort the occupations by % with PhDs (or professional degrees), things aren't too surprising for the top occupations - doctors, lawyers, scientists, educators.

A few surprises pop out: 4.9% of tax preparers have PhDs as do 4.7% of funeral directors. 1.5% of umpires and tour guides. 1.1% of "amusement and recreation attendants" (carnies?), 0.2% of butchers. Talk about alternative careers!