I have a Hayward SP-1082K skimmer weir which I just bought the other year. The foam insert got pretty fouled up during last swimming season with pink slime, etc. It seems that the inserts are next to impossible to find without also having to buy the door. I checked in a local arts and crafts store but their foam and styrofoam is of the wrong size and also it is that stiff, crumbly material and so probably would not hold up long. The material the skimmer weir insert is made of is much more flexible.
I did come across one or two places on the net that sell the foam, but it costs just as much as buying another door, which I really don't need. Let me know if anyone here knows where I might get the correct type of foam.