Look on ebay for industrial filters.
You may need larger, but it's this sort of thing: http://www.ebay.co.uk/itm/2X-Carbon-...3D291709689561
The stuff was called 'Declon' and was first popularised for speakers by JBL I believe, who made the front grilles for the L100 Century model from it around 1970.
Main system: MMs/ADCs/Low output MC's/One rare Japanese SUT/One scarce British phono stage/various tonearms/hefty Japanese DD TT and hefty Japanese BD TT and small British BD TT. 4 CD players/2 jitter buster/2 DACs/Valve buffer. TVC stepped attenuator or valve pre-amp or solid state pre-amp. Current dumping power-amp or either of two Class A SS power-amp or Class A EL34 valve monos or big Japanese (part Class A) integrated. Big dual concentric speakers/Smaller dual concentric speakers/Two way British compacts and full range speakers, amongst others. And too much more to list!