I want to sell the private key of the address that participate the tezos and cosmos ico, who wants to buy it?
There is no guarantee that you have not written a script ton 24/7 server that will automatically send money when it is deposited to any blockchain address associated with that private key.
Most of those who sell the private key are for the purpose of obtaining free coins if any hardfork occurs, but hard forks rarely happen now, most of the currencies were produced for centralized chains and low-cost tokens.
You won't find anyone buying such a private key.