Amazon.com: The Buzzards Roost FlexSlide Extended Range Antenna for Garmin Astro/Alpha : Electronics
Amazon.com: High Gain Long Range Magnetic Base Replacement Antenna Compatible with Garmin GPS Alpha 100 200 200i Astro 220 320 430, Eifagur : Electronics
Folding Antenna for Garmin Astro 220/320 Handhelds - Garmin Product Store