You could do it with a 556. Just look up the datasheet. The pins on the other half of the chip have the same names and are connected in the same way as on the single 555. There is, of course, only one set of power pins.
But why do it that way? Your switch can be wired with a resistor that is added to (i.e., in series) or put across (i.e., in parallel) to the timing resistor(s) you already have. SPST push button switches are probably easier for you to find and would work well for putting the additional resistor or pot in parallel with one of the current timing resistors.
Without knowing exactly how you have connected the 555 timer, I cannot tell you exactly where to put the switched resistor. Can you post a schematic?
John