Sorry, tub newbie here. My skirt is in great shape except the holes where it screws into the tub frame. They have worn over the years and the screws now want to pull through.

They all used to have these nice brass washers as seen in the picture here:


Does anyone know where to get replacement washers like these? Or what they are officially called? The local hardware store doesn't care anything except finishing washers which won't really work in this situation.
Thanks!