There are CD's of gongs and other percussion instruments used for meditation that might be what you are looking for. There is a gong struck at the beginning of the song "Birds of Fire" by the Mahavishnu Orchestra but I can't vouch for the length of the decay..
Best Examples Of Cymbal Decays On A Recording
Pleas provide an example of any recording with an outstanding cymbal decay.
...or, any recording that gives an excellent example that showcases a decay of a particular sound...whether a vocal or anything else.
Thank you.