If the pot is used as a voltage divider, you could try using a 10kC pot and install a 3.3k resister across pins 1 and 3. That would approximate a 2.5kB. The resister across the leads changes the taper towards an audio, that's why the C taper is needed to get close to linear. It depends on the circuit though, you have to draw it out and see if that works.
Here's some more info on making different taper pots, but when you have the right value and wrong taper. With your problem, you can't get the value, which is why I suggested the above.
http://www.geofex.com/article_folders/potsecrets/potscret.htm