Answer: Gherkin is actually a slightly different species (Cucumis anguria) than regular cucumbers (C. sativus). Gherkins are small and somewhat oval, with prickly skin. However, gherkin is also commonly used to describe small cukes used for pickling, as in "I'm going to make a batch of gherkins." So, I'm not really sure what specific plant your grandpa had.
I did a plant source database search and nothing came up under C. anguria. However, there were well over 100 varieties of C. sativus. Burpee offers a number of cukes especially for pickling, including Burpee Pickler, Pickalot, and Picklebush. You can look at descriptions and photos online.
Also, you might try heirloom seed sources and seed exchanges. The National Garden Association website has a seed exchange. Go to http://www.garden.org/swaps/seedswap.asp. Another possibility is the Seed Savers Exchange in Iowa, 3076 North Winn Road Decorah, IA 52101. I'm not sure if they have a website yet, but they have been around for many years with the goal of saving heirloom seeds. Good luck!
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