Where can I find a very good power supply for a micro-atx form factor?

Odd. Micro-ATX refers to the size of the motherboard, as in its physical dimensions. It doesn't have anything at all to do with PSU that is compatible with it. PSU do have several different form factors as well but they have to do with the chassis they are installed in. If you have a full tower case then it should fit any standard ATX PSU (there are a few expections but these are generally well documented if you google your specific case) and they come in a wide array of wattage. If you need a smaller form factor PSU they are often limited in wattage by their smaller size and the fact there is little demand for high power PSU in slim/micro cases.