There are a number of data resources for economic data. It is unlikely that "disposable income" is a specific variable, as that means different things to different people, and in different contexts. You can use to estimate such things the best are:
If there is a variable called "disposable income" be certain that it measures what you want to measure. If there is not such a variable, then you can reasonably estimate it by subtracting the median income from the per capita income: median income being a rough estimation of how much per capita it costs to live a median life, and the remainder being disposable. Alternatively, if you are doing a cross nation comparison, per capita is probably a reasonable proxy, because the difference between per capita income and disposable income is likely very high.
Many of these statistics, and other sources, are compiled and available from NationMaster.com, too. That website also will create charts, graphs and some other tools for representation of the data.