Online, "hanging planter" or "hanging basket" seems to always mean ROUND basket.
How about window boxes? This one was on sale but is now out of stock:
http://www.gardeners.com/buy/h...
I found another hnager, like that but square:
http://www.greenhousemegastore...
The last link "Greenhouse MegaStore) also sells three-arm "hangers" you could use to hang a rectangular planter if you can find one.
Maybe put a grow bag in a hanger?
Or buy a round wire planter and squish it into an oval?
Edited to add:
I kept looking, and Lee Valley Tools lived up to its reputation for having cool things that are a little expensive.
This hangs on a wall or fence, has compartments for multiple plants, and some watering gadget.
http://www.leevalley.com/US/ga...
Lee Valley's high-end stainless steel hanger for any shape container:
http://www.leevalley.com/US/ga...
And a pricy, fancy, rectangular "Stratford Planter" that looks like wrought iron:
http://www.leevalley.com/US/ga...
