Foxley gives the manual procedure for sizing the lost+found directory on the aforementioned page 52.

I have the 1986 edition of Fielder's and Hunter's UNIX System Administration and it does not mention any such command in its discussion of lost+found in chapter 3. It references AT&T Unix System 5 Release 2 (or 'UNIX 5.2' as the book puts it).

But Google Books tells me that their later 1991 update, referencing Release 4 and with an updated title to match, does indeed mention mklost+found. So that looks like something that appeared in Release 3 or 4.