Yea, on the larger bikes 350, 500 and 650s, they were called bathtubs. Not a great success at the time and most were junked, subsequently they now go for funny money. Likewise a Sports cub or mountain cub. A lot of 'no interest in bikes, but it's an investment' type of folk have jumped onto the Classic market, hence the price of auld bikes (including classic jap bikes) has rocketed. Around 5-10 yrs ago you could have picked up a Tiger cub for around £300-500 now your talking £1k for a rough one
Another thing is the year. 1964. Two years ago I was turning 50 and as a gift to myself I wanted a bike registered on my birthday 21/04/64. I had planned ahead and spent about 2 years before this date looking for one with no success, but I also noticed that there weren't too many 64 (B Reg) bikes generally
If you head over to Britbikes forum you'll get a load more info and help
http://www.britbike.com/forums/ubbthreads.php?ubb=postlist&Board=4&page=1