3 ways: Constantine in middle watchtower will sell you some for 25 source marks you need to complete a few specific quests before that, check in your event in on duty menu first you should have a quest for it. There are a few arts you can buy in one of the vendor in middle watchtower, it will cost you Quarks. Some specific quests will reward you a few arts aswell.
Are you trying to replace as in use your old ones to feed into your new ones? If that's the case, I'd wait till another double xp which is possibly 6 months away since we just had one. But you'll lose half of the total xp if you feed old into new today. Better choice right now is to just use the small amounts of nth to level the new ones up to 120 and put them in when ready. Save the large chunks till double event. Save up all source marks because it takes close to 1500 per artifact to go 0 to 200.
