When I looked very briefly into the subject, as I was looking for some damping material to use in my tube preamp/phonostage, I contacted Gelmec who were very helpful and professional as a company. They will send you a small selection of samples if you request it.
They have different formulations which will suit different applications and I am sure they have a product that might be quite useful in your application. For turntables, you could try the solution used by Romy (by coincidence I use the same principle but not the Vibraplane he uses) which is air suspension. It might be maintenance heavy, keeping the structure level, but nothing that is too difficult to achieve, even if you were to try to build the contraption yourself. I will send you some pictures of my air suspended platform if you like...
As for the liquid silicone damping Paul is talking about, as in Townshend's turntables, I think this is to use with tonearms. It is something I have been hoping to try someday...