My Walmart is like that, too. I have to be very specific about what I want, or bring in a label or box-top, because they have no clue. I have used the Monojects, I really like the fact that they glide well with no "sticking" but I have a terrible time trying to get all the air bubbles out of them - there is a small chamber between the body of the syringe and the base of the needle that always gets a bubble that I cannot get out. I have wasted A LOT of Lantus fighting with it!
Any pharmacist should know what you are talking about if you tell them you need U100, 3/10 ml insulin syringes with half-unit markings. They come in 2 different needle lengths (I personally like the shorter needle) and different gauges (I prefer 31 but my Walmart only carries 29).
@babyBoo You're absolutely correct, it is very important to know whether you need U40 or U100 syringes! She is using Novolin so she would use U100s.