Octane boosters work... they increase your level by .1 but they don't mix well with gas so you'll have "octane pockets" which won't be too good for your engine. Go with what musicsurfman said and use toluene. It's a common additive for people that make their own 100 octane from 91(Cali)/93(Anywhere else). Do a google search and you'll be able to find the exact formula/ratio.
Also, the other countries may seem like they use higher octane, but it's not that much greater because of the way that they measure octane, which is different from us.