I think you could buy the prismatic lense material from one of the companies that sells LED lights, or an industrial plastic supply..
I bought it from one time from Lambert Ent, but I saw recently that they don't sell just the material anymore.
Clear lense + red bulb won't work well.
HiTech sells the lense material,
You could probably get the prismatic clear from an old light fixture and bond it to a peice of red plexiglass (like what those guys are selling.