The slumping housing market could get a $200 billion boost from new immigrant home buyers if mainstream lenders start using alternative methods to score credit, a national group of Hispanic realtors said Friday. Creditors like Citigroup Inc.'s Citibank see recent immigrants as a growing market niche, but those who lack Social Security numbers or legal status in the U.S. are often rejected by the three major credit bureaus. A handful of new credit reporting systems already used by 200 real estate brokers, community groups and mortgage counselors nationwide allows them to calculate risk by evaluating a prospective client's utility bills...