How to buy multiple licenses of an add-on for a team?

First, just to clarify, you're talking about plugins or extensions, right? Not Creative Cloud products themselves?

Currently the Exchange Marketplace doesn't support paid licensing for teams or enterprises; you need to reach out the to the developer of the plugin (the Exchange requires developer contact information) and get an installer or ZXP file to deploy to your team. You can then either deploy it via the Admin Console, use our command line tool for installations, or use a third party installer like Anastasiy's Extension Manager. CCX or XDX files can be double-click installed.

If it's a free extension that's listed on Adobe's Exchange Marketplace you can deploy it through the Admin Console to your Creative Cloud Team or Enterprise organization.

Some third-party marketplaces like Toolfarm resell plugins and support more complicated licensing options, like floating licenses or render-only node licenses, but they tend to specialize in video products (After Effects, Premiere Pro).