I'm also searching for the largest sink that will fit in a 30" base. I came across the Kraus KHU100-30 and people are saying that this fits into some 30" sink bases. See the comments on Amazon. There is even a photo of it fitting snugly into IKEA's 30" base cabinet.
http://www.amazon.com/Kraus-KHU100-30-Undermount-Stainless-Kitchen/dp/B0032BYM4Y
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