Could you explain what you mean by that?
That is, access to what exactly should they block and what transaction attempts do you refer to? I don't really know what you mean but that would obviously be against Bitcoin principles anyway. As I understand these efforts at cracking the private keys, you just download the whole blockchain to your computer, then run a key generating code and see if the public key you thus generated matches any in the blockchain. If it does and it has balance (the wallet it corresponds to), then you hit a jackpot. So what are you going to lockout here?