As you specifically reference purpleish azaleas, my most recent favorite is the Poukhanense. It has a pale lavender color which I find quite stunning. In the sun it has a reddish cast which makes its' blooms even more interesting. A smaller variant which might be good for edging larger white azaleas like GG Gerbing might be the Elsie Lee (same color but double blooms!).

Examples of darker purples would be Mildred and Amelia Rose. Amelia Rose looks good paired with smaller Pleasant White azaleas.

I like to plant a hedge of smaller azaleas in front of larger ones along short paths. This strategem might work well for you as well.