Pickings are pretty slim because the only vehicles with 6 on 4.5" bolt pattern are the Dodge Viper, the Dodge Dakota from '94 to '04, and the smaller Nissan F-alphas (Frontier, Xterra, Pathfinder) 2005-present.
There are vendors selling aftermarket steel wheels:
the problem is if you search by-truck for these Nissan Frontiers, they don't list them. Why
they don't list them for the Frontier I couldn't say for sure, but I can think of two reasons. First, no manufacturer has formally tested these wheels on the Frontier, so they don't know if they fit, or second they have tested these and have confirmed that they don't fit. And even if they do fit, a Dakota-fitting (or Viper-fitting) wheel wouldn't have the same center hole, so you'd want to find a hubcentric adapter to move some of the load from the lugs to the hub.
Wheel fitment is harder than it used to be, especially with modern clearances between disc brake calipers and the wheels. It's possible that the Dakota's hub mounting surface sticks out further so the calipers end up more recessed under the vehicle, making for better clearance to the backside face of the wheel. In that case you'd have to run wheel adapters even on the same bolt pattern and size, which might not be terribly cost-effective.