I've been trying dozens of plus vintage style dresses from Amazon to see which ones fit larger bodies. Several brands (and cuts) are far too small for me, but as of right now this one from GownTown has a ton of stretch and even though it's a XXL, it fits me easily as a 22/24. I would imagine it would fit a 26 as well!
Sweater in 3X
Dress in Grey/2X