Not sure if this should go here or in Large format.

Do they make an equivalent to 667 (the ISO 3000 B&W pack film) in 4x5 sheets?

Secondly, where the heck do I pick up a 405 back? I can't seem to find them anywhere online. I'd like to get a polaroid back for my pinhole camera, and for the cost, I think I'd rather go with the 405 and pack film over the 545 and 4x5 sheet film, but I'm drawing a blank on the 405 backs.