Hi
@greera and welcome!
Arrow Group Industries, the maker of your greenhouse, was established in 1962 and eventually became Arrow Storage Products. They were acquired by ShelterLogic on Nov 23, 2015. From what I can find, it appears they no longer produce greenhouses. Of course, that is not good news for you.
You might want to contact ShelterLogic and explain your situation. Perhaps they might be able to help. Another alternative would be to find a metal fabricator who can make the clips for you. Finally, you may just have to be creative and "invent" another way to keep the glazing in place...a thin wood/metal frame screwed into the post might be an alternative.
Good luck, and let us know how you solve this problem.
Jim