Now I am trying to find it in my old hard disk
1. Have you made RAW copy/backup of your old hard drive? It's important to prevent any deleted data accidentally overwritten.
2. Have you tried using file recovery software to look for any deleted data?
I analyzed the file and found the encrypted date is 6000 bits
You need to explain this part better, since 6000 bits probably refer to length of RSA keys or size of encrypted data rather than date.
and I need a private rsa key with specific id key and my file is 165 MB
165MB file? What kind of file you're talking about? I'm sure Bitcoin-qt and wallet file generated by Bitcoin-qt have smaller size.