Garden Web has a listing by broader category (ex: bamboo). They also have forums on specific topics where other knowledgeable gardeners could probably assist you. (Ex: check the "edible landscaping" forum for help on locating edible plants; the "fig" forum for help on locating a specific variety of fig.)
But the most "niche" kinds of plants are still going to be more difficult to find.
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I got this tall by not having enough crisco in my diet as a kid. This ad looks like it had plenty of shortening:
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