Simply get Dragon Kazooie and try to shoot Fire Eggs. You will never run out for obvious reasons.

Enable the "Double egg carrying" code and go to "Madame Grunty's Fortune Telling Booth" with full Fire Eggs. Keep going in until she has given you extra Fire Eggs five to six times. Then, go to the Inferno as Kazooie alone. Kill your self two to three times. You should now have unlimited Fire Eggs.