I used an appropriately sized flathead from a electronics repair kit I owned. I also was not able to locate a suitable bit. I thought a tiny spanner ( 2 prongs) bit would do, but alas…
My most recent set had the flathead in (was also doing an imac repair and needed a larger variety of pentalobes):
It’s every bit as cheap as it looks, but since those blasted pentalobes die with each attempt on a repair pretty much, I am not looking for fancy. Stupid Apple.