I think there are likely many jewelers who can replicate the Whisper Thin! I've definitely seen others that look quite similar, although of course it depends on how thin you're looking to get. Many jewelers certainly offer the same setting for 1.5 mm but I know the RC will go as thin as 1.2 or 1.3.
Wow, 1.2 or 1.3 is so thin! I think 1.4mm is their standard size, so 1.5mm isn't too far off.