New referee

Yes Allan you can, As long as you have your badge number you can go to the club shop at Hampden or online and pick up any kit required.
I've got the SFA Referee kit 2014 from a friend and I've asked if it's okay to use and was told that's fine with it. Was looking for referee training kit
Yeah wearing old kit is perfectly fine, no one expects you to go out and buy brand new kit as it’s expensive. Other options you can purchase the standard kits and iron on the SFA badges, works out a lot cheaper