It sounds like you would like to print labels for 300 of your contacts. I would recommend creating a group, then adding the contacts to the group as you come across them with this article:
Contacts (Mavericks): Group contacts
Create a group or folder
- Select an account.
- Click Add (+), then choose New Group.You can also select contacts, then choose File > New Group From Selection.
Create subgroups or subfolders by dragging a group or folder to another group or folder.
Add contacts to a group or folder
Select one or more contacts and drag them to a group or folder.
Contacts in an Exchange account can belong to only one folder at a time. Any contacts not in a created folder are in the default Exchange Contacts folder.
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