The Z cars had rear struts/springs from 1970 on. Not sure before that.

Talk to feral here (or contact him through www.datrats.com.au). He can get King springs for the B310, maybe some struts/shocks also not sure. I've seen aftermarket struts/shocks on ebay periodically, normally real cheap ($30 per pair roughly). Can't remember if they were front or rear.

Also if you're in the US, www.rockauto.com lists several struts and shocks for the B310. KYB for the front and back and some other cheaper ones. They only have front springs though, not sure of the brand.

Good luck. Suspension is what I'll probably tackle on my B310 after my engine rebuild is finished so post here if you find something interesting.
michael

ps put your location in your profile so we know where you are. it helps when giving info like this.