6 round steel magazine in .222/.223
I know that Tikka made a 10 round magazine to fit some calibres in the 595 rifle but not sure if they did it for .222/.223rem. The 10 round magazines were and are extremely rare.
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.
If you do a search on this site you may find something on it as I'm sure that others have posted on this very subject or something similar in the not too distant past and have even included photographs on replacement bottom "metal" for the 595.
The oe tikka .223 mag holds six, with a little modification it can hold 7 but only on an open bolt, the replacement bottom metal needs the action milling to accommodate the mags to fit, and re-proofing