I have bought from both pharmacies in person, and tons off amazon. I usually use 27ga 1/2" insulin pins. I still keep a box of 1ml leur lock barrels (the twist type you mentioned), and a handful of diff size leur lock needles on hand.

The ones with the flip-top safety are too bulky imo. I keep one of these on hand, so I just clip the needle and the flip-top isn't needed, then toss the syringe in the trash.