New Player looking for supplies

Hello, I'm looking to get into SW Legion. I get that the unit cards come in the boxes, but is there a way to get extra copies of them? Can I buy the cards on ebay or etsy? I haven't found any on sale. (except for some promo ones that are like $50)

TL;DR: I'm looking for places to buy the Unit Cards, Upgrade Cards, and Command Cards
(Sorry for the incorrect flair, there wasn't a "question" flair or "help" flair)