Replacement window/Sliding door roller assembly.

I have a custom patio enclosure and the Sliding door became difficult to open and close. The is no manufacturer noted on the door/windows. One of the rollers had a disintegrated bearing. Can you help me find a replacement assembly or even just a roller. The unit is 3 7/8 inched long and a 1/2 inch wide. The roller itself is 7/8 inches in diameter. Both the windows ands door use the same roller assembly.