For some reason Citizen didn’t give model numbers (i.e. 67-xxxx) to two of their chronographs. One is in the 8100 line, and carries the case number 4-900014. There were two versions and I’ve managed to acquire one of them:
This one was made in May, 1972:
I’ve added a pic of this one to the article – https://sweep-hand.org/citizens-vintage-chronographs/ – where you can also see the other type which has a silver sub-dial.
The other model without a model number is a colourful Challenge Timer, more usually called a ‘bullhead’ these days. This is the 4-901096:
Sweephand's Vintage Citizen Watch Blog 
Hey there, hope you will still read this after all this time but how would one go about finding this watch? I really love the first one you pictures and I can’t seem to find it on either English or Japanese auction sites. Thanks in advance!
Hi Mike, thanks for visiting my blog. I’m afraid these models are very hard to find, and searching eBay and Yahoo Japan are where I’d advise to look for one. It surprised me how few chronographs there are for sale on Yahoo Japan, not many of any kind come up very often. The other thing you could try is a ‘want to buy’ post on the relevant forums, such as the SCWF. Stephen