There is a ready made graphite spray... Spray a layer, sprinkle with ground ferite. Dry, repeat.
I wonder if you used a spray paint gun and a bead blaster gun , how good a product you can make with very thin sprays. Both very cheap from harbor freight and you would not really care about the things you typically care about for paint job quality, and maybe a third spray paint gun with primer or some kind of filler compound if you need physical spacing. I can see myself building some kind of RF lasagna if I could wield two spray guns akimbo like a john woo movie, maybe with a foot switch on a heat lamp aimed at my mold to solidify it after each coat. It would take a long ass time but you can do it? Or maybe you can make a X/Y scanning laser to solidify it, some kind of UV cure foam binder maybe, i wonder if you can emulsify UV cure adhesive, it cures mad quick.
I wonder if you could grow trapezoids of the stuff using 3 spray guns and alot of time. Ferrite powder has to be cheap since you can buy inductors for so little. I don't think it makes sense to shield the really low frequencies at the foam level, you should just use mu-metal backing plates, they sell it alot for EMI crazy people that want to protect their houses from their junction box.
If you get the process down you could use solenoids to automatically trigger the guns, all taped together (like ripleys flame thrower pulse rifle), if you get the motion down, so aim it, and it gives you a few seconds of graphite loaded UV cure foam, then a few seconds of ferrite powder spray, then turns on a big UV led that you aim at your masterpiece before hand, all foot pedal operated, so you can do thousands of operation without destroying your hands, so long you get the rythem down. Or if the process dynamics are not too much of a pain in the ass, you might be able to mix it in the aresol phase by activating the sand blaster and the spray gun at the same time. It seems like you would need to try it to see if you can tune a good continuous distribution. Hell you can even easily do voice controlled solenoids, I imagine this would go on like 0.5mm at a time between cures, or slower... maybe throw in some stiffening strips of carbon fiber or some shit every so often so its strong.
You could actually make a big ass piece then cut it easily with a bandsaw to make your cones, rather then trying to grow it in cone molds.
Does anyone know the proper ingrediant? I can see something of very high quality being made this way without difficult shit like distributing everything in expandable foam to grow properly, it might be a pain in the balls if it starts sinking to form heavy layers. Unless you spray expandable foam real light, let it grow a bit and then spray it with the other stuff with layers...
I am convinced commercial pricing would hammer the hobbyist on buying this stuff. It might not even be that complicated.
I found that air-powder distributions are really good, even with large particles. If you are ever doing a garage epoxy floor from home depot, and you need to distribute those decorative flakes evenly (which will make it look great even if its all stained and fucked up from acid/solvent damage etc), I found the best way is to get a small leaf blower and put the flakes out in a cupped hand and just hit it with the leaf blower, works real nice compared to throwing them into the air, you get this nice evenly distributed cloud.
Maybe mixing UV cure adhesive with something like cabosil (fumed silica) would make a decent space filler that would kinda be foam like even if its not really foam. Cabosil is horribly voluminous for its weight. Or maybe aerogel powder of significant mesh can approximate foam where foam should not exist. I don't see commercial UV cure foam spray solutions.
Cabosil should be transparant to UV light some what, so maybe you can use a regular UV adhesive spray, then a dusting of cabosil mixed with the E/M conductors, if its not possible to spray the cabosil while mixed with UV goo.. might actually be more uniform then real foam without all the engineering crap to figure out foam behavior. Or maybe even using fiberglass 'powder' as a filler?