I don't know that the name is actually museum putty but I found what I bought at Hobby Lobby. Maybe if you explain what you want to do with it they can tell you what they sell. I'll see if I can find what I have.
I just did a websearch and found these. In California, they call it earthquake putty. Amazon has the clear stuff, also. The first one is neutral, but th second is the gel I like because it does not show: