Can we get all weapon illusions in Lohner’s Emporium by opening chests?

I notice that I still have several locked orange weapon illusions per hero(Not DLC illusions). However, I have played 800 hours and owned more than 100 red illusions. So the title question.

Do I need keep opening chests? Or I can only buy them to unlocked?

You can pull all the orange illusions from chests. They are suprisingly rare, though. (Only exceptions are Grail Knight’s weapons, but you already specified no DLC weapons.)