Is there upcoming events that will give proof of hero?

I feel ya dude, 0 proof of hero right now and just rolled Musashi, she's now stuck at lvl 60. The closest event that gives out proofs is unfortunately a while away - the summer 2018 rerun. The (kinda) good news is that after that we get a string of events all with proofs, but you'll just have to farm them normally until then.

As for farming locations, according to this: https://grandorder.wiki/Proof_of_Hero
lubbock in E Pluribus Unum has a decent drop rate (29.6 APD)