What size fuses are you looking for? For what purpose? If you have only 1 solar panel or 1 string of solar panels in series then there is absolutely no reason to install a fuse between the panel(s) and the controller.
If you have more than 2 panels or strings in parallel then you do need fuses on each string.
Square D QO series breakers are rated for use in DC circuits up to 50 volts. This makes them usable for 12v and 24v solar systems but not 48v since a 48v system will be over 50v when charging. You can get QO breakers and panels at any Lowes, Home Depot, or electrical supply.
Or, you can get purpose made DC breakers. MidNite Solar and Outback both sell them (and some others I'm sure). Most any solar equipment dealer should be able to help.