I'm surprised to find that I can only find 4-5 listings for Citrullus lanatus (watermelon) in GRIN, ITIS and every other database I can find online.
The ATP Plant Database has nine pages of cultivars under Citrullus lanatus.
And the ATP Watermelon database has 838 cultivars
Do they just not care about cultivars? It seems like a rather ivory-tower attitude if part of their intention is to be useful to people who, for example, want to distinguish among Bok Choy, turnips and rapini!
Is there some other taxonomic database online that would let me search for cultivars? I was looking for seeds of Citrullus lanatus 'Schochler', and had trouble finding references to it other than an NC State University publication.
I haven't gotten much joy from USDA / ARS / GRIN / NCGRP / PGRCU either, but I have an email in to the Research leader of the S-009 Technical Committee (Southern region germplasm)). If part of their mission is to make rare seeds available, they sure hide their light under a bushel!