I've never searched for a seat, and don't have any idea what's available. I'm guessing not much, but could be wrong.
Here's what I'd do in your place. First measure the max available footprint for a replacement seat, the height of the seat from the floor, and what floor clearance is required. Then carefully check the underside to make sure there would be no problem drilling 4 new holes through the body, at the corners, keeping in mind that you would need to replace the slider track with the one from the new seat. Then go to a U-pull and check the seat on as many vehicles as necessary, until you find something in decent condition that you like, and will fit into the Aveo seat area measurements. Removing the replacement seat might be a PITA, and a battery angle grinder would be nice to have on hand. Installing into the Aveo shouldn't be a big job. You could probably haggle a good price for one of these.