Try any electrical wholesaler. They'll carry the boxes as well as the connectors. The thing to remember about anything "outdoors" is that it has to be rated for it.
Here's a link to Thomas & Betts products (Red Dot Weatherproof Boxes):
I used rope light around my pool cage for several years. It was exposed to Florida weather and in contact with the ground (well, with the lanai floor anyway).
More than waterproof, you need a good GFCI extension cord. This will protect you better than any waterproof box. Unfortunately, no matter what you use outdoors short of a NEMA cabinet, sooner or later it's probably going to get wet inside.
Outdoor extension cords with heavy duty, rubber (probably neoprene though I'm not certain) end fittings don't require a box. They are available at most electrical supply stores, some hardware stores and probably at Home Depot or Lowe's as well.
Rather than add a GFCI extension cord (my cable plugged directly into an outlet under the covered part of the lanai) I installed a GFCI breaker in the electrical panel. Since that breaker powered outdoor ground lighting and some of the pool equipment, it seemed best to just protect the whole affair. Ground fault protected breakers are also readily available from the same sources.
You just need dry. What I use to keep the rain off is a short stick to keep it off the ground and covered with the inverted bottom of a 2-liter bottle with the top cut off. Keeps the top couple inches of the stick dry, cheap, EZ to make....
Cabling-Design.com Forums website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.