Last I bought Spicer joints it was from an independent big truck parts place. Anopther option is most any/all driveshaft shops that are any good use and sell Spicer stuff. Just ask around, some local parts place will sell them, shouldn't be hard to find.
Looks like you've done a fine job with your shafts already, I sure wouldn't take them apart just to swap joints that aren't broken/worn yet.
Grigg