You need to use Redemption - as they are not exposed in Outlook's Object model
I'm not sure how useful it would be - or how much time you'd save using a macro over using the built in Junk > block sender / domain commands. You can put the block sender button on the Quick Access Toolbar to make it easier to access.
You don't want to add both the domain and the sender to the blocked list - there is a limit to the number of entries, and you'd waste one. (If the messages are in the junk email folder, you dont need to block the domain - the filter knows they are spam.) But you also need to be careful not to add popular domains or risk blocking messages you want to receive.