ASA offers a Catamaran Course, I think it is ASA114. The problem you will find is most of the schools do not have Catamarans and therefore don't offer that particular course. I just checked a couple of ASA schools in MA and did not find any with the course.
You might look at how far you are willing to travel and check ASA schools within your circle. There are course prerequisites to taking the Cat course as well. You may find something in Lake Erie, and I know it is offered in Michigan at BBYC.