You want the last years growth of rowan or apple for this sort of thing. Spindle tree is also supposed to be very good but I have no experience of it, more than a bit rare around here . Maybe some of the archers can offer advice too.
Basically something without a pithy core, so that rules out willow or elder.
The straight shoots from last year's growth just need to be de budded, peeled and waxed and they dryout slowly and stay sound.
The problem is making knitting pins fine enough (probably why the earliest ones are wires) my oldest ones are made of bone, though horn is very good too for short ones such as the sets for gloves and socks.
It'll be interesting to see what you come up with