A good place to start is ebay - check it out frequently - an ABDL seller who does custom work should be able to make such a garment *
* take a look at the sellers history and auction items for quality reference.
And just as a closing thought you could do this on the less expensive side by simply wearing tights over plastic diaper covers - no sewing required !
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Look a little further in this forum section for the Posts to: Looking For Frilly/Ruffle Tights for an AB !