Anything goes for a fermenter really, as longs as the recycle codes are <1> and <2> just look for what fits in your space.
These are a couple popular alternafermenters talked about on here all the time.
Aquatainers available at most big box stores- Very popular with no-chill brewers, since they can take boiling wort and can vacuum seal as it cools, but can be used as a regular fermenter as well..
And vittles vaults from pet stores.
A few places are carrying <2> 3 gallon water jugs, especially with the BPA bans over the years water jug manufacturers are going with hdpe and pete jugs these days
Plastic Jerry cans that are meant to hold water can be used,
Collapsable water jugs work too.
Walk through any big box store and look at storage containers and water containers and you'll find plenty. Then get a rubber grommet, put a hole in it and attah an airlock.
is a great source as well.