What medicine is close enough to focalin (dexmethylphenidate) to replace it, if you can't find focalin (dexmethylphenidate) to buy?

Many. There are many medications that are used for the same purpose as dexmethyllphenidate (focalin (dexmethylphenidate)). The closest relative is methylphenidate which is generic or branded as Ritalin or a longer acting form concerta. Talk to your doctor who prescribed the focalin (dexmethylphenidate).