Go to your Subscribers list.
Click on the tag on the right side that you want to share.
Click the checkbox at the top of the list of the subscribers to "Select All" - if you get a message that it's only selected the first 30, click the link that appears to select all of them.
In the "Bulk Actions" dropdown, choose Export. ConvertKit will email you a link to download a .csv of these subscribers. You can then share that file with someone else.