replacement mirror roller

Hello,
We purchased a home with 2 mirrored sliding glass doors [very heavy]. One of the doors has a broken roller [I think that is what it's called] and I have been unable to find a replacement part.

Following is a photo of the part. I admit my phone is not the best, so if you need a better photo, I will have my wife take one to send. This photo was the best of the one's I took and is on the side that is not broken so I drew a line to estimate how the break looks. The top of the door is barely visible at the bottom left.

Again, I will get as much detail as possible, but just wanted to find out first, if you have something that may work.

Thanks for your time.
Jeff