Eridian weapons can be looted from higher level weapon chests. The Engineers and Badass variants of the Crimson Lance also take a liking in eridian weapons and can drop them. Guardians, being of eridian origin, also drop eridian weapons. There are 3 types of 'blaster'. One fires small fast bolts.(mercurial blaster) Another fires medium sized balls which move slower than rockets.(ball blaster) The other, again, shoots small fast bolts that move up and down in a wave motion whilst flying thru the air.(Wave Blaster) In my experience this was the most rare Eridian weapon, with the cannon seeming to be the most common.