Small, hollow, thick-walled tubing needed

This sounds a lot like the last post about tubing, and I admit that's
where I got the idea, but I need some tubing considerably smaller in
dia.

I need 3/16ths od with a thick enough wall to do an external thread
at each end, yet hollow enough to allow oil to drip through. These
are to be used on my little Merlin engine project, and I'll need 28
pieces about 3.5 inches long, 3/16 od, with some sort of oil passage.
The hole is to allow oil from the camshaft area to drip back down
into the crankcase. Yet these are actually hold-down studs for the
cylinder block (including cyl. head) so they have to be strong enough
to be torqued. The engine is 1/4 scale.

Any thoughts on where I might easily buy such tubing? I have checked
the hobby shops, and it's a good start, but the hole is a tad big for
me, so the walls are not quite as thick as I'd like.

Thanks in advance. Tom Kay.