Well,
in this thread, it was described that Honda's change-over from JIS to ISO metric threads was "effective from the start of production of all new motorcycle models first produced after the beginning of 1967." I believe the CA160 went into production in 1966, so I really don't know whether your 3mm, 4mm, 5mm and 12mm fasteners are old JIS or newer ISO pitches.
That said, are you interested only in NOS original fasters, or will you accept new fasteners? If you learn that you have standard ISO pitches, you can buy fasteners from
Bolt Depot, or similar on-line sources. If you try Bolt Depot, scroll down a bit and you'll see "Metric Fasteners" on the left margin.
If you have older JIS threads, then you'll either have to find NOS or used fasteners for any 3mm, 4mm, 5mm and 12mm fasteners. For other sizes such as 6mm, the new ISO metric fasteners will work.