I got it all from Amazon.
The battery is the USB C charging extended battery. Searching "BTECH BL-5L" should bring it up one with 7000+ reviews. You can find others selling some for cheaper but I wanted to make sure I got the real deal.
The antenna is a "Genuine Nagoya NA-771 15.6-Inch Whip." It should have over 18,000 reviews. They REALLY extend your range.