The user makes certain selections, such as Company, Country and Year. After that it wants to browse within the selection 'Month'. From current month to next month or back to previous month. How to realize this with for example buttons?
You have just to create a list box of months (as you already created to Country or Year) and use 'drag-and-drop' over the listbox or the CTRL or SHIFT keys to select more than one month! Is your doubt simple as this?