When I googled "natural preservatives" a link to fromnaturewithlove.com came up that had a lot of information Using Preservatives to Extend the Shelf Life of Your Products - FNWL
If you google any of the others that are of interest, you'll find where you can buy them. Pretty sure it will have to be online.
Citric acid serves a few purposes in food/hair products. It's considered a natural preservative (wouldn't expect it to keep your FSG from spoiling too long) and it lowers the pH. Hair has a lower pH (on the acid side of normal.) The reason that the preservative is near the end of the ingredient list is that only a small amount is used/needed. I think I read that it's around 1% of the product.
3a (Corkicelli), highlighted, fine, low porosity
modified CG, since April '07
CG since 3/11/08
HGs: Curly Kinks Satin Roots, Curlycue ReNew and Coil Jam; homemade FSG and okra gel; soap bars; DM MiraCurls Curling Gelly; UFD Curly Magic; Shescentit LIs; Sevi conditioners; Botanical Spirits Puree, CJ Repair Me