best way to collect bombs

[1969venus]

What is the best possible way to collect bombs if you play the game on an android device?
I just recently started playing after being gone for almost a year. I was pleasantly surprised to find new things to do and other ways to obtain rare dragons. I am however having the hardest time collecting enough bombs to go into the mine to obtain materials to craft dragons. I was 10 pieces shy of getting the idol dragon. 22 from the azure and well, the list goes on and on. Any ideas or suggestions?