It *is* hard to come by material about Thomas Ince, but you might try the
following article (available through interlibrary loan, if your local library
doesn't own the journal):
Mitry, J. "Thomas H. Ince: his esthetic, his films, his legacy."  _Cinema
Journal_, v.22, no. 2, 1983, pp. 2-25.
A local library might also help you with the Yallop book, since it's probably
out of print (I did a fast check and didn't see that title or anything like
it by the author).  Good luck!
Jeff Clark
James Madison Univ.
bitnet: fac_jclark@jmuvax1
internet: [log in to unmask]