Wow how did you manage to do that lol.
It's a mesh filter rather than a felt type of filter so they don't normally come with spares, no? Since they're not meant to be replaced (or to fall out), unlike the RE0's.
Pretty sure the filters on the POPO are pretty much acoustically transparent, or at least supposed to be. Wouldn't be too worried about the sound.
When I removed the tip on the left side, I could already see that the mesh was glued on wrong (the ring of adhesive plastic holding the edge of the filter onto the bore had shifted) and was sticking out of the side of the bore. When I fitted in another tip the tip caught on the bit of mesh sticking out and made the mesh come off.
The right side had a treble peak that became stronger after the mesh was removed. It was already stronger with the mesh than the left side without the mesh :?: So it seems I can conclude that the drivers themselves on this pair of Popo were not well matched.
FR graph: black is left side, red is right side.