Even some local banks in my area have had there commercial investments curtailed. Peter gives good advice about local banks though. That is where you MAY find a HELOC or a commercial loan. It is possible to also do blanket financing on the commercial end with some local banks, but from my experience in my most applicable market at least they want 5 properties minimum and preferably more.
I think you need to make sure that you are buying right and creating actual value with the rehab, and then sell the duplex to another more passive investor as a turnkey property for a decent gain. Make sure you establish an LLC and that it takes title before you sell it so that you can get all tax benefits of a company.
Talk to a CPA that specializes in RE to find out what to do to reduce it and repeat the process. As you gain more property and thus income, you will likely be able to get financing based on your company's income, not your personal situation.
Go talk to local commercial officers now to find out what would be best to do. I would also suggest that you establish an account with the bank or banks you want to do business with, both personal and company. If they see the income coming in to their accounts it should be easier to get the loan eventually.
Remeber when times get tough it forces the tough to get creative.