Do like me and buy them
invite black lizard Xer to Bareshade's fair. He sells lots bombs.
Xer is to be found near Corrupted Lake in forgotten temple, when you sneak around there. During a day he's usually out to look for some ingredients, so that's the moment you can find him. Have a cleansing water, would be a good start.
But he's available after you complete good lizard's tribe ending.