Aw, what a lucky Goosy!! You need to PM IainUtah for sure. Shes got a pet goose working on foot issues right now, and they turned out to be spinal I think. Shes found a good vet, after seing a flop, and her goose "spirit" is much improved. I think both she and CelticOaksFarm may both be good choices. Come to the goose rescue link
https://www.backyardchickens.com/t/686015/goose-lovers-please-help/260#post_9393213 where you can talk to Iain and Celtic both. Just go there, post your link to hear, and ask everyone there to come and look and offer adice. Iain just got geese this year, but she's now a goose rescue mama, and has about 60 geeese, and has educated herself very well. Celtic is very very experienced, more than me for sure, and can proboly guide you well too.
Now that said, any fish store or
walmart will have cheap boxes of charcoal in the pet section. Just call
walmart and ask, then go get some. If you call a drug store, they maybe also have some. Its very commen. Not the kind you burn, but its similar. I've used it many times, and while I can't always know if it helped, I'm positive it won't hurt at all. And, there are times I feel its whats made the difference.