Does anything drop Iron Heart Recipes?

I've already learned the Gold Heart Recipe, I just happen to have a ton of Steel Ore that I was hoping to put to use, haha. It's too bad I wasn't here for the Legends Event. I had no idea Iron Hearts only lasted a week though, I assumed they all lasted two weeks. Hmn.

Thanks for the answers! I'll keep looking around too. Seems strange that nothing drops them.