How do I get blue essence faster?

Couple days ago, I tried Riven from the free champion rotation. She was so fun to play and pretty good. However, since the champion rotation will change, I won't be able to play her. I want to buy her for 4800 but only have 2260.

I tried to level up, and disenchanting some champions, but am still behind. I don't really want to refund my champion either!

Are there any other ways to get blue essence faster, besides leveling up and disenchanting champions?

I also have another question, is there even a way to get a ton of blue essence at once?

This might work, but no hacks please

thanks