I would think anyone back then with enough money could get a master woodcrafter to make any size and shape knitting needles for them. As for metal ones, that would be difficult pre-industrial revolution. Possible but difficult, for sure. Maybe iron... cast iron. I haven't done a lot of reading on this yet, so don't quote me on it.
Actually, thinking of making metal needles is reminding me of the coat hooks I made just before Christmas. Really, to make something like that, they would either have to heat up and draw the metal through a round hole in another object that's harder than the toughness of the heated metal or they'd have to heat it and hit it with a hammer, turn, hit, etc. until it was the correct shape and thickness. If they used the second way of doing this, the created item would end up lumpy or square... even if just a little bit so.