i have dropped two holy bonds from doing regular attacks for xp, and prolly close to 20 epic bonds.
now with that being said, if you are only spending energy here and there, it will take a lot longer to get these limited bonds
when i compete in the weekly tourneys, 30 million xp is not uncommon, that is 1,000's of attempts and some weeks i get nothing, but im sure there is a law of large number randomizer floating around and the more times you do something, the odds will increase that you will drop an epic or holy bond
i would like to see more holy bonds in tourneys though, we need upwards of 200 holy bonds for a chance at a max set of oranges