Where can I buy a rasp cutter Specially for milling polysterene

[marbles]

Ok so its a bit of 4mm or something. Horizontally or vertically down the centre? TBH need a bit more information to discuss solutions.

If its just a single thickness sheet of ply and you know the depth can you not set up a cut path with a 2 flute just to cut the ply then have another toolpath and cutter for the foam? I have 12mm 2 flute endmills up to about 100-120mm which will take down that ply in just a few layers. it all depends how deep you need to mill.