Finding rental housing for a low-income family in Anchorage is hard. If you’re part of a family of more than four people, it can be nearly impossible. The availability of affordable rental housing has been at a crisis level here for years, said Rhoda Myers, who works with Catholic Social Services’ program for homeless families. The situation is harshest for large families who face monthly rents comparable to mortgage payments and fierce competition for the few units available, say social service providers, economists and would-be renters. The consequences are overburdened shelters, and families who spend almost all of their money on rent or hopscotch between shelters and motels.