Here is some parts info for you to find what you need by measuring your old one and gives you part numbers to ask for at the parts counter of your choice.
http://www2.dana.com/pdf/K350-1-DSSP.pdfWith the right catalogs likely you can do the job that any good parts guy can do for you.
I'd be looking for a better parts place if the ones you usually use can't even find a u-joint for you.
I prefer Spicer U-joints, but don't think NAPA sells them here, so ask who does in your area.
Grigg