I use to buy old picture frames
like the Google image below, that were in disrepair with cracks and broken off or missing pieces of plaster decoration. I would give them a good “stiff” brushing off, then mix up a batch of Plaster of Paris and “gob it” onto the broken area and with a stiff artist’s brush, finger, whatever, … recreate the design as best I could. Then I would use a good quality “gold” spray paint to repaint the entire frame. The designs on the frames are most always so “busy” (varied & different) that the “fix” doesn’t have to be perfect and one has to look really close to see where the repairs were made.
I offer this info for anyone who has such an old dilapidated frame.
Don’t throw it away. Recondition it and I’m sure you will be pleased with the results. Now I use to cut my own glass “to fit” the frame if the original was broken or missing but I suggest you purchase it from a local retailer.