To my knowledge no one has found where he introduced legislation.
He didn't. Because of the subprime lending mess and lax regulation Obama claimed to have sounded the alarm two years ago and said last year he wrote to Paulsen to to make sure he understood the magnitude of the problem (imagine that) and called on him to bring the stakeholders together. It was then that McCain, as an aside, said he too warned congress.
He did more than warn and should have been more forceful in explaining that he co-sponsored the Federal Housing Enterprise Regulatory Reform Act of 2005, S. 190. urging quick passage of GSE regulatory reform legislation. This from Hot Air shows the role he played