I get them at WalMart, but sometimes you have to ask them to open the box since we've heard a lot of times where they've said they don't make them with 1/2 unit markings
I got mine at Target--they were $12 for 100 count. I took the used syringe and showed the pharmacist what I needed--he opened the box to confirm it was the right kind.
Those are great prices! I paid $19 for 60 at CVS. Make sure you check them before you leave, mine were in packages of 10 and about half of them were 1 unit syringes and the others were .5. I took them back and they exchanged them for .5 units.