First of all, keep in mind that if you can't find the exact value for a resistor, you can buy several resistors and hook them in series. This way, their total value is equal to the sum of each resistor. e.g. if you need 5k and the store doesn't have it, you could buy 5 1k resistors and hook um in series to make 5k. You can do the same thing with pots. You CANNOT do this with capacitors. Caps must be hooked in parallel for this to work.