Apocalyptic retail therapy

The people desire commerce. (Me, I am the people.) I’m currently just a big piggy bank running out Pharloom hoping to avoid losing my thousands of rosaries to foolishness on a runback.

I’m partway through act 3, but all the vendors still don’t have any new items and I haven’t discovered any new ones.

Is there a quest/boss that unlocks act 3 purchases? Is there even anything to buy in act 3? Should I just invest in gun?

Thank you for your time. Not looking for major spoilers. Just maybe a point in the right direction. Although if there’s nothing to buy that’d be nice to know so I can relax about losing everything. But that seems unlikely given the new deliveries and such.