Found a seller of PT809c magazines, $19.99 each. Gunmagwarehouse.com
Bought one taking the chance it wouldn’t fit in my TH9c.
Item # 5-10809C-13
Item: Taurus PT809C Compact 9mm 13-Round Magazine
It did fit my new TH9c, except I had to file the upper side of the square hole that fits the latch by about 1/16”.
One bonus find, is that the magazine plate has a more pronounced “pinky” ending and feels more comfortable than the new ones.