Don't know why this is coming up after six years but you're right. The top nut is the same as the rear axle nut (36 mm). I got mine at OSH for around $3.50 when they cleared out some Craftsman sockets.
The lower spanner nuts need something different. Suzuki sells it for a bunch of money. Komotodraggin.com sells it for less. Turbosuzukis sells it for still less on ebay.uk. Or you can make one like this