I imagine we're not in the same country so this is of relatively little use, but I had a gander and it does look like they're in pretty low stock across the board. Some of the places that are out of stock have the price in the range of £20-£50. The only ones that are in stock are like £90, which speaks to how short in supply they are.
I can't offer any advice unfortunately. In the past, I've found hard-to-source parts on sites like AliExpress, but I would personally feel nervous about doing this for a battery. I'm likely over cautious, but it's hard to tell what is sufficiently legit, and batteries are scary.