I've just had a quick look on aliexpress, but not come up with much:

1X3flutes 20mm HRC50 Fine powder tungsten steel alloy cutter for aluminum milling-in Milling Cutter from Industry & Business on Aliexpress.com
Wholesale New HRC 60' High Speed Milling Long Shank A2~4S 8 150 2,4 Flutes Micro Grain Carbide Square End Mill Cutter-in Milling Cutter from Industry & Business on Aliexpress.com
6*101*140mm lengthened 2 flute end mill, customized wood milling cutter, carbide spiral router bits, for foam acryl cnc machine-in Milling Cutter from Industry & Business on Aliexpress.com

Maybe you'll find something with a bit more searching, or you could ask the last seller to make one as the ones he's listed appear to be specially made? For foam I expect a low number of flutes would work better.

Remember the deflection of a cutter is roughly proportional to its length cubed, and inversely proportional to the diameter raised to the power 4. You therefore should always use the shortest cutter you can, with the largest diameter. That's why the 6mm diameter 100mm long cutter is probably only going to be able to cut foam - e.g. with the same cutting force it would deflect about 110 times further than a 25mm long cutter the same diameter, or 18 times more than the 16mm cutter from APT (assuming 120mm and 170mm unsupported length respectively).
Having said that, you're only cutting foam so the cutting forces are tiny which means you can get away with a lot.