It's not circular, but the Czech and German army surplus 5L cans fit inside the 15" rim of my Samurai spare tire, and take a standard NATO spout.
Like this one for $15:
http://cgi.ebay.com/Army-Surplus-Czech-5-Liter-Jerry-Gas-Oil-Fuel-Can-/190393026832
HTH,
D
Like this one for $15:
http://cgi.ebay.com/Army-Surplus-Czech-5-Liter-Jerry-Gas-Oil-Fuel-Can-/190393026832
HTH,
D