Bulbagarden

i expect you can trade... the problem may be finding someone willing to trade ><

I can, just not right now, maybe after school
Should I post a trade request thingy for Ash-Greninja? (I plan to use Moon because it doesn’t have my real name unlike Ultra Moon and I strongly value my privacy)

Might not be the answer you want to hear, but if you have a hacked 3DS, you could get the Demo and play through it and still get a legitimate Ash-Greninja. I know it's not the most authentic way to get it, but aside from trading, it's probably the most legit way to get one. It's not like the demo costed any money or anything either. As for trading, I know a lot of people near the end of the Eshop's life cycle did get some spares, but they are probably not east to bargain for. I have one, but only one, and I'd like to keep it if possible, but if you have any older (Gen 7 below) event Pokemon I'd be willing to negotiate

Another possibility I just thought of, I have a hacked 3DS and could get you one through replaying the Demo, but I understand if that's not what you're looking for.

My 3DS isn’t hacked for obvious reasons so that’s out of the question. The demo was definitely free ^^

You can keep yours. I don’t think I have any event mons from Gen 7 below, unfortunately-

As for replaying… Might as well at this point. ^^