Warmoth makes good stuff, but doe to their brick s---house construction [a good thing], they might feel a little "chunky" if you're looking for a thin Jazz neck.
USACG and AllParts make "Jazz necks" a bit thinner, or "vintage".
I've been doing plenty of research for by own build and this is what I've come to understand, but I could be wrong.
I suppose some TBers with real expertise will weigh and and add to or subtract from what I've posted.
In other words, don't make any decisions based on this post.
Edit: There was a post i read yesterday that had a link to an ebay store that sells real Fender necks it seemed. I didn't understand how Fender would allow this. I'll try and dig it up for you.