If you want to stick with the Icom, which is a good choice, they have two models that are similar dimensions as the IC-M45. The current models are the IC-M422 and IC-M304.
http://www.capemarinesupply.com/prod...p?prod=M304+01
http://www.capemarinesupply.com/prod...p?prod=M422-11
Attached are three images of the physical dimensions of the three different units.
If you want something else we carry all of the Icom line as well as a bunch more.
Fixed mount VHF
Rich