Potomac Mills has a "Sanrio" store.. that's the company that makes all that hello kitty stuff.

Springfield Mall has some stores too.. I didnt know Manassas Mall had any.. but I rarely go to Manassas Mall cause it sucks and it's 5 minutes from my house.

But honestly, go to Annandale or Alexandria.. lots of asian shopping centers will have stuff. Like asian super markets will have a section for 'gifts' and they have a lot of that Hello Kitty stuff.

Eden Center is a Viet shopping center in Fairfax.. they have a lot of Hello Kitty stuff too.