Our WhisperLite stoves haven't changed much in the 15 years you mentioned above. Mine is about the same age. There is a WhisperLite/International Expedition Service kit available which I would recommend. It contains the parts specific to our stoves including the #28(kerosene) & #35 (gas) jets. bc.com can, most likely, get it for you.

You will probably need to contact Cascade Designs directly. The jet was improved in the early 90s with a shaker jet which changed the threading of the jet. You can call (206) 505-9500, or write them at Cascade Designs, Inc.; 4000 1st Avenue South; Seattle, WA 98134. They will most likely send you a new jet. None of the current Service Kits have the right jet you'll need.