While it's not complete and almost certainly not the reference mentioned in the paper, Philip Guo compiled a list of programming languages used in introductory courses at top 40 departments (as ranked by US&WN). The key result is this table:
which shows that the only functional language, Scheme, is used in roughly 12% of departments.
There are two problems I see with using this as a statement about CS education at-large: first, this is a sample of the top 40 research institutes, which may not be representative in terms of teaching habits.
Second, Guo (by his own admission) is counting both CS0 and CS1 courses in here. For example, he counts CS303E at UT Austin as an intro Python course, although it's intended as a half-semester language intro for non-majors. This may skew the appearance of certain languages in his data.
Finally, a note: in the comments section of that article is a statement that says
What we need is someone to resurrect the more comprehensive annual survey that I believe Jean E. Sammet used to do up to a few decades ago...
I wasn't able to find any record of this survey, but if "a few" means just one or two, then that might be the source you're looking for.