Only the "ready load" regular films fit the 545, and I don't know if these are still available. The only instant film that is large format, besides the Impossible Project films, are pack films from Fuji such as FP-100C, and they do not fit the 545 but do fit into polaroid pack film holders.
As Whitey said, no, there are no film types available from Fuji that will go into the Polaroid 545 film holder (I also have two of them), but there is hope. The Impossible Project people may be responding to the number of requests for a Type 55P/N replacement. There is hope. There are occasional rumors of others under consideration, but that is the only one where there seems to be real work underway.
For use in the 500 Series of Pack Film Holders, look for the Fuji pack film boxes with the "45" suffix, such as FP-100C45.
Ralph Javins, Latte Land, Washington
When they ask you; "How many Mega Pixels you got in your camera?"
just tell them; "I use activated silver bromide crystals tor my image storage media."