Canonical answers:

* Most cities/under-30 ranking areas will have eq lying around. E.g. Castle Akan, Evermoon guards, Tir-Talath guards, Catacombs in Arkham, guards in Arkham, Guards in Seantryn, Battlefields, Velkyn Oloth, etc etc. Load up on gear, go to merchants, sell. Eq of one standard guard in Seantryn is probably 8-10k, when sold fully. What happens if merchants don't have the copper? Go to the nearby other merchants. For example, Arkham + Hamsah + Balator. Or Seantryn + Aturi. Or Upper Cragstone + Dagdan.
* Farm treasure: precious stones in upper Cragstone are good for several thousand copper per tour.
* For barter with the cave of webs lady - typically, folks go to Galadon Sewers, around the thug/smugglers area and they get those odd items (pamphlet, tube, whatever). Each one of those is worth 2-3k copper, you can't sell them anywhere, but they're great for bartering.

Hope this helps. Never had an issue with lowbie coin.