i like the color of 'elsie lee'. a web search for that cultivar should produce sources for mailorder. carlson gardens comes to mind. this one blooms a bit later than most of mine but is a nice, soft lavender flower with frilly edges.
poukhanense azalea/korean azalea is another similar color (perhaps more to the pink side of lavender) that blooms very early for me.
'autumn royalty' is a darker purple of the encore group (reblooming) of azaleas.

Here is a link that might be useful: carlson gardens - purple and lavender azaleas