USP Grade Vg is what is recommended. (Pharmaceutical grade). You can find it on amazon, or through many flavor vendors. Walmart and some drug stores sell USP grade VG in either the first aid, skin care of hair section. Or look here:
http://www.bullcityvapor.com/ (Capella, Flavour Art, Flavor West, Hangsen, Inawera, Flavor Apprentice)
http://wizardlabs.us/ (Capella, LorAnn, Seedman, Flavor Apprentice, )
http://www.ecigexpress.com/ (Flavour Art, Flavor West, LorAnn, Flavors Express, Natures Flavors,
Signature (TFA), Jungle Flavors, Hangsen, Tasty Puff, Inawera, Capella)
http://www.rtsvapes.com/ (LorAnn, Capella, Hangsen, Flavour Art, Flavor Apprentice, FLavor Jungle,
Flavor West, Inawera, RTS blends)
https://www.myfreedomsmokes.com/ (LorAnn, Flavour Art, Flavor Apprentice, MFS house blends)
http://www.diyflavorshack.com/ (House blends/brands)
https://shop.perfumersapprentice.com/c-108-the-flavor-apprentice-world-of-flavors.aspx (TPA/TFA)
http://capellaflavordrops.com/ (Capella)
http://flavorwest.com/ (Flavor West)
http://diye-liquidsupplies.com/ (Capella, Flavor West, LorAnn, Flavor Apprentice,House Blends)
http://wholesale.heartlandvapes.com/ (Capellas, Flavor West, LorAnn, Flavor Apprentice, House Blends)
http://www.eliquidmart.com/ (Capellas, Flavour Art)
http://vapingzone.com/DIY-Flavoring-E-Liquid-Flavoring/cid-56-1.html (Vaping Zone VG flavor, Hangsen)
http://store.flavorah.com/All-Vaping-Flavors_c_8.html (Flavorah)
http://www.nudenicotine.com/products-page/concentrated-flavorings/
http://www.madvapes.com/nicotine-flavor-extracts/flavor-extracts.html (Madvapes)
https://highdesertvapes.com/categories/DIY/DIY-Flavors/ (Ellas, Flavor West, NF Organic, Flavor Apprentice, Capellas)
https://www.tastypuff.com/product-category/tasty-puff-flavor-drops/ (Tasty Puff)
http://www.vaperstek.org/ (Molin Berry, Inwaera, German Flavors)
PG/VG Tractor Supply carries PG (gallon)
http://www.essentialdepot.com/
https://www.dudadiesel.com/
http://www.bulkapothecary.com/raw-ingredients/other-ingredients-and-chemicals/glycerin/
Good luck.