Have you broken your brake caliper
You sound as if you need a long drop caliper. Try and measure the distance from the centre of bolt hole in the fork to the rim and also take note of the diameter of the hole if it is 8mm at the back, you need a recessed mounting although there are workarounds.
Personally, I'd go with a Weinmann or Mafac centre pull as they can be adjusted to fit a wide range of drops and give excellent braking power despite what some will say. You will require a cable hanger for the headset if you currently have sidepulls.