If you can locate them, the old Austin Craft needle valve assemblies look the most authentic as I think they bought many units from them too. They made jillions of those things and they pop up on the auction sides pretty often.
But you can use many other needle valve assemblies just fine too. OS, Enya, Fox or others for example.

Now then if you have some types of needle valve units and the center needle is missing, it is pretty easy to make one and solder it back into the needle holder cup. I found a piece of mild steel rod that fit into the needle spray bar and chucked it up on my drill press and used a file and some knife sharpening stone to shape a needle point and taper on it.

Here is where I did just that myself as I had received this engine without the needle, but I still had the needle holder.