One solution is to export your contacts from your two Outlook accounts and other Gmail account and import these contact files into your main Gmail account. This process will create lots of duplicates, but you can use Google's duplicate remover tool built inside Google Contacts to remove and merge many of the duplicates.
Another service Scrubly Duplicate Contact Remover can clean up the remaining duplicates Google's tool misses. The service is not free, but does a great job. It also imports your friend's contact information from Facebook, LinkedIn and Twitter.