Im an italian sound guy living in Mexico now after many years in Spain.
In Spain we used to work with Bostik Blu tack wich i think is exactly what you say Fred, and it´s available on amazon in the US.
I used it in cars, also because has a good isolation from mechanical vibrations, and sometimes also used it with MKe gold mics on hard leather jackets to separate capsule from the surface....really useful
I looked for something similar here but the butyl for sure did not had that characteristics.... too sticky and too many oily residues
I miss that!
If you came to Mexico bring me one of those Henkel Teroson Fred!
regards