Hi Kristin,
You have a couple of options here:
1. Add these people to a contact group in your Address Book, then select that contact group within the manual send. To do so, go to Invitee Management > Manage > Invitees & Registrants > Advanced Search > Under Agenda Items, click on the "Agenda Items" dropdown and select the quantity item > Search. Then, select all of the names, and go to Bulk Actions > Update Contact Groups. Add these people to a new or existing contact group. To send the email, go to Promotion & Communication > Email > Event Emails > Click on the email > Send: Manually > Click on the Contact Group dropdown and select the group you just created > Check off everyone's name > Send Email.
2. Run the Registration Summary by Registration Item report, then send the registrants an email from that report. Go to Reporting > Reports > Standard Reports > Registration Summary by Registration Item > Select Quantity Item and pull it into the Selected column > Run. Then, click on the item, and click Run again. Once the report processes, go to Actions > Send Email.
Best,
Julia