Wire Artist magazine had a series of articles, where they showed how to form each letter of the alphabet, I believe both upper and lower case. They did not use a jig though.
They do an excellent job of breaking down the steps, and always have nice, clear photography of the steps you need to see.
I believe they did a few letters per issue, rather than devoting an entire issue to the alphabet. Visit them at http://www.wag.on.ca to find out if they have all the back issues available.
The letters were very nice - like the gold wire names that were popular a few decades ago.
There probably aren't any jig patterns for the alphabet. One reason is because if you are doing names, each letter connects into the next letter in a slightly different place.
You might be able to create jig patterns for letter *charms.*
To make jig patterns for letter charms, I would suggest making a few dozen photocopies of a moveable peg jig (or the grid paper that may have come with it), and just start sketching each letter around the pegs, making sure to include a loop at the top of each one.
My guess is that you'll have to make fairly large letters, to avoid a too-blocky appearance. (Consider what letters and numbers look like on a calculator display - where you usually only have 6 points and 8 lines to connect everything).
Are you more interested in making names/words, or just the letters?
If you're interested in making names/words, I would strongly recommend the back issues of Wire Artist, even if they add up to fairly expensive. (Or if the back issues are gone, maybe they know of a book to recommend.)
--Polly