sliding glass door roller

I have been trying to locate replacement rollers for my sliding glass door. I can not find anything that resemble the original rollers. The roller pictured is from my sliding glass patio door, there are two of these, the roller pictured appears to have  all the little rollers in it, the other roller is missing several of the small rollers inside.  I can not find any markings on the door  or this roller to determine the manufacturer, the door is approximately 25 yrs or more old. This door was installed prior to my ownership.