Thanks to all for responding. This past weekend, based on the advice of a couple of people who live in the area, we visited a small community about 25 minutes away which is off-grid and talked to a lady there. They bought their tanks (which are HDPE) from Tractor Supply. Although I'm not thrilled about using any kind of plastic, even supposedly "safe" plastic, it looks like our best bet unless we one day break down and build our own ferro-cement cistern. The largest is 2500 gallons, and is a much more economical buy than any of the smaller sizes of rain catchment tanks/barrels that I can find on amazon.com.
Also, we are going to have a 10X12 Tuff Shed build in a couple of weeks, and from there we will start catching rainwater so we can have a supply by the end of the year. Thanks again!