Here is the rundown on availability/compatibility:
Fuji PA-45, Film holder for 4X5 Pack film
There are currently only two Pack Films offered, that
will fit the Fuji PA 45 Back, or Polaroid 550 Back
Fuji Color, 100 ASA, 4X5 Pack Film
It is rumored that production of the 4X5 inch B&W, 3200 ASA, Pack Film,
has ended; only the 100 ASA Color, remains in production in 4X5 inch, though
some say this B&W, 4X5 size, is still produced/distributed for the Japan, or Asian markets.
I'm unable to confirm this at this time.
Fuji B&W, ASA 3200, 4X5 Pack Film
Below are the three (smaller), Pack Films offered in 3.25 X 4.24 inch size,
and to the best of my knowledge, still in production for worldwide distribution.
These (3) Pack Films will fit the Fuji PA 145, and Polaroid 405 Film Backs.
Either of these backs do appear with some frequency on the big auction site.
Fuji Color, 100 ASA, 3.25X4.25 Pack Film
Fuji B&W, 100 ASA, 3.25X4.25 Pack Film
Fuji B&W, 3200 ASA, 3.25X4.25 Pack Film
The Polaroid, Single Sheet Film Backs, Model 545/545i, are totally
useless for readily available, Instant Film Photography of today.
Too large for paper weights, and too ugly for door stops...Useless!