Just hang out near BPI and McD's. Wave at every foreigner walking by like they are your friends. Then say "dollars"? The dollars mafia might not be too pleased with the competition though.
You can buy dollars from the bank. Why not? I have done it. I once asked a street dealer why, if he wants dollars, he does not buy them from the bank. He said something about exchange rate, but had no good answer. I think at his amounts, the pesos he sells would be subject to forms and identified as black money.
Here is a link to show you that you can buy US$ at BPI for 46.75 pesos BPI Forex Rates | BPI The page also states: Limit on foreign exchange that may be purchased without documents for non-trade purposes has been increased from USD30,000 to USD60,000 effective November 24, 2010. That means to me that its a pretty good rate if you are buying up to US$ 60,000