Simplex steam pipe union nut/nipple

[grandfathertyke]

Does anyone know of a source for the 5/8 x 26 tpi union nut plus nipple for the connection to the steam T? I know I could make my own, but I've got so many jobs on the go that I'd prefer to take the easy route if I'm ever going to finish this loco in my lifetime (or even the next at the rate I'm going)!

Thanks in advance,

Grandfathertyke