Is the only way to get these via WZ Commendations, so having to PvP?

I do PvP, but I've never done with a Guardian (my Artifice character). I can give it a try, but hate being a burden to the rest of the team

Just wondered if there was any other way to get them?

As far as I know, that's the only way to get them.

If you want to kit out your artifice character (assuming he's at 50 already), you could buy some legacy-bound armor (or use the event armor if you have it), acquire some PvP gear on your main, and ship the legacy gear (with the PvP item modifications in it) over to your alt.

Crafting yellow crystals is unlikely to be that useful, though. If you have a couple Tionese commendations, you can purchase a Tionese offhand with a yellow crystal in it. (All such offhands other than lightsabers or pistols will work.)