List of Mortgage Companies

Credit unions?

How will credit unions help me with my FICO score?

The same way a bank would, except you get lower loan rates and higher savings rates from a credit union.
Just having a checking or savings account at a credit union will not help you with your fico score unless you start bouncing checks and get reported to a collection agency in which case your credit will be in the toilet. If you get a loan through a credit union ( would have to be a member) then it would be reported to at least one credit bureau the same any other lending institution would report it. The main difference would be lower interest rates.
Before you get a loan from a credit union, make sure they report it to the credit bureaus because some do not in order to keep the cost down.