Usually places like autozone won't carry the specific oem vacuum lines for your car, which is likely why they were confused.
They do sell generic pieces and connections you can use to install new lines.
The only issue I've seen so far with using aftermarket vacuum lines is that (at least on the 6th gens) GM used small solid tubing for the vacuum lines and big soft connectors and T fittings. The ones you'll usually find at a part store will be a larger soft tubing and small hard connectors/T's.
A chevy dealer should be able to order the exact parts you need as well, but a lot of the vacuum lines come as large pre-assembled sets (found this out when the PCV elbow on my old '01 LS cracked and split..had to buy the whole section for it).
2004 Monte Carlo SS Intimidator #3470/4000
N*tb-3.25"mps-Gen5-zzp s2ic-1.9 rockers-TOG headers