@DenverDude555 

The AV1000 and AV2000 are only sold in pairs.

To add the adapter you would press the pair button on the new adapter and press the pair button on any of the other powerline adapters.

Here is a link that will show you how many powerline adapters you can have on your network: https://www.tp-link.com/us/support/faq/434/

@Tony  If a 2000 can not be found anywhere, will a 1000 pair up with existing 2000?

@DenverDude555 

Yes, but what will also happen is the powerline network will be set at AV1000. The slowest powerline adapter is wha the network will run at. Still test the speeds as you may not even notice.