The GM-30 uses an SMA-Male (SMA-M) antenna connector. This is the opposite of what most handheld GMRS and ham radios use (SMA-Female on the radio, SMA-Male on the antenna), so your existing HT antennas almost certainly won't fit without an adapter.

If you're looking for a direct-fit upgrade antenna, the Nagoya NA-771G (SMA-Male) is a solid choice. Just make sure you get the SMA-Male version.

The Baofeng GM-15 Pro GMRS Radio (Amazon) is essentially the same radio, but it uses the more common SMA-Female connector and is advertised at 8W TX power versus the GM-30's 5W.