I think you're out of luck on that one. Was looking for one myself, last week. Went through this entire thread:
https://www.fasttech.com/forums/vapers/t/2661745/all-bubble-glass-for-rta-and-compatibility-list/1
(Great thread, btw)
Problem is: the Serpent mini's glass at the base is 21mm, and most of them are 22 wide. With a height of 17.5mm, the only one listed with that height was
SKU 8053800. But that one looks as if the top is much wider than the bottom.