Conviction should be for everyone because it's not fair to the people who can't pvp and who don't pvp at all. The only way for people to get Conviction is by get a necklace from any minion onthe street or by a boss. Most people have the most trouble against a boss because they need the time and health in order to attack both minion and boss or in case of a battle in Khrysalis at Fort Rachias, bosses like Gevan Wishbleeder and Jovan Hopedrinker and somehow you can't do anything without blocking. This is my reason why Conviction shouldn't be only pvp.
I don't PvP yet still use conviction in the form of treasure cards. You can buy them at the bazaar. You can also obtain these cards through gardening Couch Potatoes. You can get Couch Potatoes in the crown shop or as drops in GH. Since nearly every MoB drops them in GH, I would suggest farming for them.
You can buy the TC directly from Killman Copperleaf in Zafaria for 1500 gold, in the Bazaar for 600 gold (almost always) and harvest them from gardening Couch Potatoes that are available from every mob in Savarstaad Pass in Grizzleheim.They are a really common TC so it's really not only for pvp players. Ranked pvp players just have the benefit of being able to learn it.
Or you can just buy conviction treasure cards from Kiliman Copperleaf in Zafaria. It's what I did before I were able to train for my conviction spell. I keep a healthy amount of the tc on my side deck to compliment my trained one on main deck.
Love this spell, not only does it add to your critical arsenal, but it's also useful for it's critical and stun block capabilities. And you will need these capabilities in the advanced worlds.
Check out conviction TC's in the bazaar. Anyone can buy it and they are fairly common. If you would like a guaranteed source head to the baobab crown library in zafaria.