Westmarine in the US www.westmarine.com They will ship to the UK and under the replacement of the "Type Approval" regs YOU are responsible for the set being OK for use in the UK now.
My Ratheon 551 works fine & it cost me <£100. You just have to remember to manually increase power on ch 67 as it is automatically reduced to 1W on first transmission in the US (even on "INT." channels)