You have two choices here. One, you can purchase a stacked integrated unit, Frigidaire makes one and the same unit is also sold under the Kenmore brand.

The second choice is to purchase seperate washer dryer units that can be stacked. Whirlpoole and Frigidaire both make these types of units, along with a kit to stack them. They are bigger, but the combined cost will be more than the integrated unit.

Either choice should be fine, and they do come with gas dryers.