I don't think you can find any that is 3" long. if you have a machine shop or know anyone that have a lathe machine you can make the slider as long as you like it to be. It's made out of delrin plastic with an aluminum bushing.
HEY BRO THERE ARE SOME 5 INCH ONES ON EBAY FOR SALE RIGHT NOW....GO TO EBAY.COM AND PUT THIS ITEM NUMBER IN 2462554874. JUST HAPPENED TO BE LOOKING AROUND AND FOUND THESE. THESE SHOULD BE LONG ENOUGH FOR YOU!!!!!