matching the roller assembly

I removed the aluminium sliding door and expected the assembly to be removable. As it turns out, after removing the mounting screw, I found that the roller assembly did not come out--rather it was slidable along the length of the aluminium rail.

The assembly was 2" or less long, so only had one wheel. Any Idea if this is your assembly? or whose it might be.

There is only one hardware store on island and only has the removable style off roller assemblies.

Any help to identify would be appreciated .. Thanks. Paul