Purchase package of event registrations
I've never seen anything like that done. The only thing I can think of off the top of my head:

Create the ability to purchase the package. You could do the page through a contribution page.

Create a discount code (you'd need to install the extension for discounts) that is specifically for them. Make it a 100% discount. Give it 6 uses.

Email them the code. Be sure they understand that it's specifically for them and can only be used 6 times. If they share it, then they're losing registrations they paid for.

Then they can register for an event and use the code to have it fully paid for.

This will take some manual work on your side (creating the code, sending it to them).