Start | Run | Charmap
Ensure font is Arial.
Scroll down the list until you find Greek Small Leter Alpha, Beta, Gamma,
etc.
Copy these characters to clipboard then paste them into your Chart Title.
Use the Characters property of the ChartTitle object to access
individual characters within the text of the title, and change
the font of the desired characters to "Symbol".
Dim ChtTtl As ChartTitle
Set ChtTtl = ActiveSheet.ChartObjects(1).Chart.ChartTitle
ChtTtl.Characters(Start:=4, Length:=1).Font.Name = "Symbol"