You can even get it at walmart or any pharmacy. a lot of people who make their own juice use it.
though cutting down with just vg may not be what you're looking for. I think theoretically you want to cut down with a 0mg nicotine version of the juice. When you add plain vg, and if you add enough to a certain threshold, it makes your whole bottle of juice have a pure-vg ish taste... and take it from me. it doesn't taste good
but if you're just adding a bit, you can give it a try- since it's only like $4 for 100ml