After a bunch of research when I did mine, I picked up a 5/8 wave, no ground plane, GMRS antenna from Laird. If I recall correctly, the antenna, cable and connectors cost almost as much as the radio - but it works pretty well for me. It also tuned to the 275 fairly well.
As I recall, I did not see much love for the Midland antennas when I was looking.
This is it:
The Laird B4505CS is a 32 inch black base loaded mobile UHF whip antenna with NMO base and spring. This antenna does not require a metal ground plane. This omnidirectional antenna offers 5 dbi gain and 100 watts max power and operates in the 450MHz - 470MHz range. Compatible with GMRS repeaters...
www.arcantenna.com