Lower Retainers for Multi-Track Aluminum Vertical Sliding Windows

My sister lives in apartment with four multi-track vertical sliding windows. On the window panel closest to the living space, there are what I call plastic retainer tabs in the lower corners of the windows to aid in maintaining alignment of the windows as they slide up and down. On these windows, the plastic tabs have worn and broken off on three of the four windows. There are no markings on any of the windows that I could locate. The two black retainer clips shown on the attached picture are the same. The narrow width of these retainers are about 5/16". Unfortunately, I didn't measure the long length of the retainer. The retainers are secured in the lower corners of the windows with screws that extend from the lower corners of the windows through the notches in the retainers. If they are available, I would like to order 10-12 replacement retainers. Any assistance that you could provide would be greatly appreciated.

I checked my pieces on the windows I am dealing with and the dimensions match the ones in the supplied drawing. I'd definitely be interested in buying some replacement pieces for my windows. Please advise on the steps I need to take to order the replacement pieces. Thank you for your help with this request. JB