You can buy and 3 or 4 button remotes on ebay (3 is correct) with the picture of the locks on them, not the one that say lock/unlock. Programing is easy just follow the steps in the owners manual.
To find the code for the keyless entry: remove the jack cover at the rear left side you will see a box looking forward. Get a mirror and a light and look at the side facing inward torward the center of the truck. There is a 5 digit code in fairly big numbers. If it is real dirty you can take it out, that is what I did when I bought my 98.
Scott