Now that our resident encyclopedia has identified the gun others can do a bit of googling...
Here's a pic of some various Nambu pistols and a link to a site on the history...the type 94 is bottom right. The wooden grips on yours marks it as probably a mid to late 1944 production...Japan's manufacturing resources were becoming severely strained at this point. Is there a number stamped on the rear of the frame 18 or 19.X? 18=1943, 19=1944...x=month.
I checked the numbers and it says 19.12 so I assume by what you've said that it was made in December of 1944. Again thank you so much. The gun has a leather holster with integrated magazine carrier. Unfortunately it we don't have a magazine for it...yet. Will this be a difficult find/expensive?
Once in a while you will find the magazines on ebay, or gun auction sites such as gunbroker or auction arms. You can also get modern reproductions from companies like this one: http://www.ammoclip.com/J/japanese.htm They are not common, fairly scarce, as is 8mm Nambu ammo. And no, nothing else will substitute for 8mm Nambu. When shopping, make SURE is is for a 94 Nambu- there ARE others.