Depends on how legal it needs to be.
maybe something here--> http://www.molex.com/molex/products/family?key=lighting_accessories&channel=products&chanName=family&pageTitle=Introduction
Good luck,
CD
I've done it with 4 square boxes and cord clamps - something like this
http://www.galco.com/buy/Halex/16912B?source=googleshopping&gclid=CPrO_vTL29ICFQQNaQod-KYHDQ
Not sure how well those standard outlet boxes will hold up to being dropped on concrete, but real "pendant" boxes are EXPENSIVE !
I have used metal handi-boxes in the past.