Do they have a washer that fits a king size comforter?

Yes there is a few machines that definitely would fit a king size comforter for sure!

I am able to wash my 21' boat canvas in the large front loading machines they have there. I imagine a king size comforter would be totally manageable, but I guess it depends upon just how thick and puffy it is.

Yes

Olivia - our largest machine will wash the equivalent of 5 loads of laundry. So odds are - Yes we can handle your comforter. Bring your item in and one of our attendants will assist you. Thank you, see you soon! MCL