I hear you! Trying to keep everyone on the same page is like herding cats; nigh on impossible lol.
Do you have other pets? I ask bc if you maybe had a more solid relationship with a small animal vet they might be able to personally recommend a large animal vet. Or maybe a horse friend / previous trainer that could recommend a vet / farrier? I’m not saying that your current vet isn’t lovely, but rather IMO it’s crucial to have at least one actor in the soap opera that you trust implicitly. And I can see how it might be hard to have that level of trust with providers that are new to you; particularly if your pony has been having issues!
My vet is human and thus I expect him to make mistakes (in 20 yrs he’s made one), but I trust him completely to be straight with me, do his best and to have my animals’ best interests at heart.

and I actually just tried to look on the individual products’ labels but they didn’t say! However you all have me convinced to just try increasing copper and zinc anyway so as soon as I’m out of the Mega Cell I will do that.