I don't know that you can "extract" these emails as a group, but you can change your view to list the reminder field and sort the emails by it.
(1) On the left navigation bar, highlight the mailbox you wish to change.
(2) Right click the title bar where it lists the names of the fields being displayed. From the menu that appears, choose the "Field Chooser".
(3) In the field chooser box that opens up, change the dropdown menu to show "All Appointment Fields".
(4) In the field chooser, scroll down to find the "Reminder" field. Click and drag it out to the Title Bar where all of the other field names are displayed.
(5) Click the X on the field chooser box to close it.
(6) To sort all emails in that mailbox, click the name of the field in the Title Bar.
(7) To remove the field from the view, right click the field name on the title bar and choose "Remove Column".
Note: you will have to do this for each mailbox containing the mail items you are searching for.
You can also create a custom advanced search folder to display all mail with a reminder set to ON, then create another one to display all mail with a reminder set to OFF. But, you can not create one with a criteria of just "reminder", no matter if it's on or off.
