Midweek hair pulling special!! (Easy one I'm sure for those in the know!)

I'm looking to fill a combobox with data from a range

But...

(please check the attached workbook to see layout)

if I was to enter A in cell A2 then the combobox would populate with the data from range E2:E4. Again, If I entered B in cell A2 then it would populate with range F2:F4 and so on. Ideally It would range from A to L and the corresponding ranges.

Can any of you kind folks give me some pointers??