So yes, basically I am looking for a pre threaded tube with two pre threaded end caps for the top and bottom
you don´t need two end caps , one for the bottom is enough , the top is mesh.

the body itself

with my second design i went another route to be able remove the headbasket . you´d need a 50mm brass tube for the body , and a second 52x1mm brass tube for the headbasket . the before mentionend method is the easier one .

i still have some bottom endpieces for a 50x1mm brass tube , and mesh in different sizes , however you would have to source the brass tube yourself , which actually should be the easiest part.
if you really wish to do your own body i could help you out with the mentionend parts .
Not so long ago there weren´t that much possibilties to buy manufactured bodies and a lot of people build their own bodies .
now people design pcb´s to fit cheap donor mics.
there must be thread "guerilla mics " or something like that . take a look .