SDA gave you two solid recommendations. Both would require you to order them (most likely) though. Animal plastics, unless you live close, is online only. Petco or petsmart can usually order in exo-terra large sizes, but also may have what is usually called a "40 gallon breeder" (also 36" x 18").
You could upgrade both your ball python and kingsnake to animal plastics enclosures, then just stack them on top of each other. Depending on the type of kingsnake, they could use the room as well.