I would imagine that those brass sleeve turnbuckles are .5mm od, which is the standard size most people use rather than the smaller and readily available .03mm od. I think the .5mm looks ok in 1/32 and 1/48 but thats just my opinion.
I would also think that it would be quite hard to thread suitable rigging through a .3mm tube let alone a .2mm one. You certainly wouldn't be able to double it back through the turnbuckle, which again IMO creates a neater finish.
Good luck with your search, I would be interested in seeing any results.