Sir Reginald Wingate, a British general, is said to have described the Bedouin as “an untrained rabble, most of whom have never fired a rifle.”
Google search for "most of who have" returns about 2,70,00,000 results. While a similar search for "most of whom have" returns about About 70,20,000 results. I understand though, from Laurel, that a more reliable approach would be to either consult the Corpus of Contemporary American English or Google Ngram Viewer.
The problem with the sentence fragment is that it does not sound right substituting "who"/"whom" with "he"/"him".