I still want to find at least 2 different public keys (better different private keys within the bitcoin elliptic curve order) which lead to the same bitcoin addresses 
Based on the birthday paradox, you're likely to find one if you have more than 280 addresses. That's a bit over 1024 addresses. Let's call it 50 YB. Once you're there, all you need to do is sort it and you'll easily find a consecutive duplicate.