The search for the origin of the 'scuba dolls' or 'winky dolls' continues. A friend of mine found two more similar dolls on eBay. One has slightly different ears than the ones I have. It must mean that this character has been in production for a while and has gone through a small style development. Unfortunately those sellers can't tell anything about the background either (but thanks anyway Cathelijne!). My pal Leendert found a inflatable one. This doll was made in Japan and looks a lot younger style-wise than it's vinyl siblings.
Browsing the internet in search of information is fun but takes loads of time. So my next step will be to write an email to Cressi -see former post. They have a nice history summary on their website, from the start of the company in the 1930's to present. Even interesting for those who don't dive. With a archive like that they can perhaps point me in the right direction.