I already went down that rabbit hole, and swore the whole world was gas-lighting me (pretty sure they are again, but it's also that late hour when I'm ramping up systemic meth levels).
One thing, the needle isn't the part that's luer-lok. That's the syringe, usually threaded for 3mL (ie., "lok-ing"), or slip-tip for 1mL (ie., just "slip-ing" on that tip). Needle that screws on a 3mL syringe thread can slip just fine onto a 1mL tip (and that's for an emulsion-based drug that requires plenty of pressure).
But since only tonight in double-checking was I vindicated that non-insulin 30G x 1/2" x whopping 5mL exist, a box of fifty is [cheap], (There is some catch, I swear, with these fucking things) maybe you could fill me in on the length insistence? I'm not sassing you at all, and understand there's a difference between 5/16th and 1.5 inches. But to find something apparently as elusive as the Great Non-Diabetes Thirty-Gauge Needle, 6mm v. 8mm wouldn't be worth mentioning.
If it helps, I'm not sticking myself, just the dog. Not intravenously, either. California-American veterinarians will tell you such a needle hasn't ever been made that didn't come attached to a proprietary pen of some kind, at any length, 29, 30 or 31G. Didn't tell vaguely-smelling-of-drugs me this, either, but my MediCare-approved-drug-reeking mother, who has a script for the dog.
(Clean-needle-and-syringe sourcing is something we do actually allow on the forum, at least for now.)