As someone else already mentioned, !anticonsumption@slrpnk.net is a good bet, but it’s still not as active as other communities.

I’d suggest also looking into:
- !zerowaste@slrpnk.net / !zerowaste@lemmy.ml / !zerowaste@europe.pub
- !buyitforlife@slrpnk.net / !buyitforlife@sh.itjust.works / !buyitforlife@europe.pub / !buyitforlife@discuss.tchncs.de / !buyitforlife@lemmy.world
- !degrowth@slrpnk.net / !degrowth@feddit.nl / !degrowth@europe.pub
- !fixing@slrpnk.net

As all of those are frequently intertwined with the movements to either buy nothing, or reduce how much you absolutely need to buy in the first place.

For something outside Lemmy, if you haven’t already I’d suggest checking out the group aptly named the Buy Nothing Project, as they’re an incredible resource if you want to find things in your community others are willing to give away, or want an easy way to give away things you no longer need that doesn’t require having a yard sale style table setup or coordinating giveaways through Facebook posts. (*though they do have Facebook groups for different areas for those who don’t want to use their app*)