The fine thread nuts are probably going to be special order items. If you have a specialty fastener store around you might check with them or online. Do you have any walk-in machine shops around? What you are looking for is very easy to make, less than 10 minutes, if they have hex stock on hand. Of course, they would most likely want to charge a minimum shop charge of $65 . :shock: You might try calling a hobby shop or 2. Something like that may be used for some of the larger RC airplane control adjusters.
Check out www.fastenal.com
5/16 x 24 x 7/8 inch long - zinc plated steel
5/16 z 24 x 1 inch 18-8 Stainless steel
5/16 x 24 x 1 inch 316 Stainless steel
They get non-stock items in fast, saved our shop often.