Alca and I both posted possible solutions on Stackoverflow which I will not crosspost here since they use unsupported endpoints.
In short there is no good[1] fully supported way to provide to query a channel’s emotes given a channel name or ID. I hope this is an area that is improved with Helix.
[1] There is an old v3 endpoint but that does not allow you the option to retrieve image sizes above 28x28.