I would just call the places you purchase plants from and ask for some containers. In a lot of cases resellers do not 'pot up', they simply sell what they get from suppliers. Places that grow their own are a better bet.

However, even the Wal-Marts will have plants die and have no use for the containers the plants were in so they just plant them in a dumpster. Just call around and you should score before too long.

If you are anywhere near Watertown you can have all of mine, dunno what I have as I would have to look in my shed, but I save every pot I get even though I will probably never use them again.