Do you have part numbers for any of the Atlas or MTH cars you listed?
MTH has a good search feature on their product locator page. You can search the Premier line for Twin Stacks or Husky Stacks and get several pages of results.
http://mthtrains.com/prod-search/twin%20stack%20?f[0]=field_product_line%3A3934
http://mthtrains.com/prod-search/husky%20stack%20?f[0]=field_product_line%3A3934
Atlas likes to hide their past products from potential customers so they don't have a functional search feature to their web site.
Atlas have made half a dozen production runs of Gunderson Twin Stacks. Change the last digit for the 3rd and following runs.
http://www.atlaso.com/ogundersonstackcar.htm
http://www.atlaso.com/ogundersonstackcar2.htm
Only one production run of Maxi IVs has been announced by Atlas so far.