Fighting dragons tips

[bukimi]

I want to get access to hiring dragons on Montero.

To do it, I have to clean a cave with lots of dragons.
There are 5 stacks of 10-20 dragons of different kinds (black, red and emerald green)
Even stoneskinned red dragons (80% fire res) lose almost half of hp from one black dragons' hit

I do not know what units I can bring to defeat them.
I do not have dragon slayer spell and did not find any to buy. (yet)
My current leadership is 7500. Impossible mage + losses acceptable.

Maybe I am trying much too early??