I've seen 2 for sale secondhand in the UK,in the last 18 months the first was badly damaged from gigging(beyond reasonable repair) and the other was well over the sensible asking price and the guy wouldn't budge,and for what he was asking,I may as well have bought a brand new one...
Lack of models secondhand,are possibly down to two factors,firstly i doubt A6 was sold in massive amounts due to the price so there would be few availible secondhand and also maybe your right in that the few who did buy them,are relativley happy with them so are reluctant to sell....
There a belter of a synth but given its 6 year old now its way overpriced,and the price has only dropped around £400 since its release,I'd buy one new if they became sub £1k,there just too expensive given that most synths are taken out of production within 2 years nowadays
I'm prepared to wait till the right model/Price comes along...Its just a matter of biding my time...