A P&L statement, tax returns (Schedule C will document this for you in the US), or minutes from your annual corporate meeting (with yourself, I assume) including a statement from your treasurer (you) about incorporating a statement of the dates, payees and amounts of distributions.
Bank statements seem like corroborating evidence of any of the above; I'd give the P&L statement a shot first. They're easy to throw together and along with bank statements, should meet the criteria of "real proof" you're being asked for.