Kent Shafer , Jan 01, 2012; 07:35 a.m.
There was a third-party battery back for the F36—the REMOPAK—which was actually introduced before the genuine Nikon cordless battery pack. More information here. I don't know that you're any more likely to find one of these for sale without the F36 though.
There more practical paths to a motor driven film Nikon, such as an F2 with an MD-1 + MB-1 or some of the later non-pro level cameras, but if you really love the F + F36 combo (which I do), it might be a good idea to go ahead and spring for a second F36 with the cordless battery back. If nothing else, you'll then have a backup F36 in case the first one quits working, which they sometimes do. Of course, each F + F36 combo has to be individually calibrated by a qualified technician so that will be an additional expense if you switch motors.