You really aren't going to find something accurate in a store, though you can make some modifications.
The asymmetrical part is a really unique design that will be nearly impossible to replicate off the rack. you have a few options, though:
1. Say "screw accuracy!" and just buy a red maxi skirt somewhere and add the buttons
2. Say "somewhat screw accuracy!" and buy a red maxi skirt and then add lines of piping, similar fabric, etc. to create a similar effect
3. Buy two skirts, cut one to create the asymmetrical part, and then modify the one underneath to create the effect
To get it totally accurate, you'd have to make it yourself, but if you don't care about 100% accuracy, then either wear a bought one or modify a bought one. Whichever way you go, however, keep in mind that Kanaya would never have anything poorly sewn or with trim tacked on awkwardly, so if you go the modification route, be sure to do it impeccably.
This is the closest I can find off the rack. It's not sold in stores and seems to only be in plus sizes (not sure what size you wear), but the wraparound effect is similar enough to Kanaya's skirt to be passable.
This is another similar one, this time not in plus sizes (again, not sure what size you wear), but it appears to have a bit more volume than the previous one, so it's not as accurate, but still passable.
This vintage skirt is a good color, length, and fabric, and it already has three white buttons, though it lacks the asymmetrical detailing of Kanaya's skirt. The wraparound style is still decent enough that you can get away with it.
Good luck with the cosplay! Be sure to post pics when you're done.
Just make sure you do Kanaya justice! A wraparound style is probably the closest you will find to her asymmetrical design off the rack, so I hope that works out for you.
