International brand patio door about 20 years old

Thanks for posting. From what I can see, your roller resembles the 81-139, which is used in International Doors. Take a look and see if you think this is what you need.

Alternate image for 81-139

Great. All orders can be placed through the online store. From the 81-139 shop page, you can simply click "Add to Cart," and then click "Checkout" at the top right hand corner of the screen. Don't forget to set the quantity you need. Let me know if you have further questions.