Replacement parts for plastic thumb latches that hold storm windows in frames

The custom storm windows in my house, installed by a previous owner, are 26+ years old. Their frames are fixed, but the windows themselves can be removed and replaced with screens each summer. The small plastic latches (about 10 per window) have deteriorated and broken over time. I do not even know what to call them in order to search for replacements and am hoping you can help. Thank you.