Hi Bob. You could try the library but your best bet may be to head to the big city and look at some of the books at home cheapo, lowes, payless, and sutherlands. They all have a rack of paperbacks. I stand there and thumb through a lot of them to see if any designs catch my eye. Then some only have pictures and no plans so they aren't worth buying.
I've started to do a basic gate post since ground heave seems to move them around and then the gates won't open and close right anymore. Put 10' 4by4 posts on either side of the gate buried as deep as you can and still get the height that you want. Then take a couple of 2by8's or 10's about 6" or so wider than your post spread. Cut notches out on each end so they set down over the posts so the posts will never spread or narrow. Take a jig saw and cut a curving design along the top with maybe some type of design towards the middle if you want. Anyway that is easier than an arbor.
Steve will be along with some ideas. Wick is putting together the ultimate web site for plans at http://www.zyworld.com/TheWick/ Maybe you will find something there. Good luck. Post back with any other questions.