Is there a list of the more cold hardy Alstroemerias?
Here is some general information on Alstroemeria from North Carolina State University Extension, which indicates they are generally hardy to 23 degrees.
The Royal Horticultural Society’s A-Z Encyclopedia of Garden Plants, edited by Christopher Brickell (DK Publishing, 1996) says Alstroemeria aurea and A. ligtu and their hybrids are able to tolerate brief drops in temperature to 5 degrees Fahrenheit.