Beretta USA are selling 6 shot magazines so if you have friends in the states or are over there at any time that is where I would try. As for 10 shot magazines (if they ever made them in .223 in the first place) they are rarer than unicorn poo so the chances of picking a Tikka one up are almost nil.
I think that a couple of companies had a go at making 10 round magazines that fitted the 595, one company certainly in Australia did anyway, but I wouldn't know where to start looking other than the internet of course.