Retracting wheel for patio screen door.

Hi. This wheel is for a patio screen door for a house built in the 1950s. There are two stationary wheels on the door and two like this, which retract into the channel to allow you to put the door on the track. The wheel is plastic and the housing is metal. I have not been able to find a similar part at a regular hardware store and am hoping you can help me.

Thanks,
Colleen