On Sat, 18 May 2013 14:22:56 -0700 (PDT), Gerry
wrote:

I am looking for an oddball size dienut-9/16"-28. Can anyone direct me to a source or perhaps someone who will custom make a dienut this size? It will be used for cleaning up existing threads, not cutting new threads. I really do not want to try to make on myself.....

Try your local gunsmith. It's used on gun barrels. Oh, here ya go.
$26.44, delivered. (hmm, + $15.25 to UK) Google is your friend:
http://www.ebay.com/itm/9-16-28-Thre...-/150989525615

--
The Road to Success...is always under construction.
--anon