A 29g needle will be hard as shit to get test thru if it's on a 3CC barrel. If it's on a slin pin, you should be fine as long as you're using a CC or less per shot.
You could always get a local PO box for cheap to get your pins shipped there.
It's not illegal to obtain syringes. Sure, it's suspicious... but you could always say you ordered them so you can pop pimples with them if it REALLY turns into an ordeal. (I've had dermatologists do this)