Where can I purchase the seal for thermal pane units?

Where can I purchase the seal for thermal pane units? I would like to try to completely rebuild my thermal pane units of various sizes, just for the challenge of it, and of course to save money. I am unable to find who sells these seals as a separate item. Every search turns up companies that will repair the unit, or will provide me with complete thermal pane units, or I find videos of people drilling holes in the glass to remove the moisture, etc. Somebody obviously makes the seals and sells them to the factories that make the thermal pane units, but I cannot find a single one. Any links to a supplier would be appreciated. Thank you.