If by Kona muslin you mean Kona cotton Natural, Hancocks of Paducah ships it, I have had several bolts in the last few years. It comes in the usual 45in width, also in 120in for wide backings (just ordered three yards of that at $8.98 a yard!) It is by Kaufman, so I presume is the same.
It washes beautifully, and comes up nice and soft. I have used it throughout my Jane Stickle quilt as background.
www.hancocks-paducah.com.
They have a website, which I don't find particularly user friendly, but that might be just me, but if you order anything, you can request a catalogue to come with it. That's lovely to browse through, though you want some of everything!