Not using a nmo limits your options. Browning 450MHz-470MHz UHF 3dBd Land Mobile NMO Antenna https://smile.amazon.com/dp/B00IDTJ2EA/ref=cm_sw_r_apan_glt_i_R2PG1ETETD6SCFAQHP5P
You can get a reasonably priced mag mount with an NMO mount, and then just get the antenna separately that fits. I personally have this Browning that is great for the price. Note that you'll still have to tune it using the swr meter but that should just be a matter of trimming the whip until swr is in line.