I know you're talking about printers, but I'm having the same problem with my Canon scanner and ended up on VueScan's site. They have software that will allow me to continue to use my perfectly good 8800F scanner when I have to replace my MacPro5,1 with a new iMac.
My day-to-day non-critical scanning is all done on my Canon printer and I have an Epson Perfection V500 for work requiring higher quality. It's 32 bit so, when I am forced to move to a newer OS, I'll definitely be looking at VueScan.
