If the bike had a threaded fork, which has I'm guessing might be the case since you said "old", you can replace the fork with a plain ol' rigid fork. I've found that a lot of bike shops don't seem to carry them in stock for 26" wheels anymore, but you can order them from places like Niagara Cycle if need be. They start around $20. To get the right fork, you'll need a few measurements from your existing fork: the diameter of the steerer tube (1" or 1 1/8"), the length of the steerer tube, and the length of the threaded part of the steerer tube.