MM do sell the IOS in 16oz. I have a swatch on my desk. Their website has most of their swatch book on it. There is also an e-mail link if you want to e-mail them any questions. They have always been prompt with a response when I have e-mailed them. They are a great company to work with.
The URL for their highland cloth: http://www.martonmills.com/range/dept/6
The contact URL: http://www.martonmills.com/contact.html
Have fun!
Sara
Who is now not sure whether to go with the 16oz or 13oz cloth thanks to Steve's and Chef's review!!