For home canning, jar manufacturers no longer make 3-gallon mason jars. Jarden Corporation, the makers of Ball, Kerr, Bernardin and Golden Harvest jars, manufactures half-gallon canning jars.
Vintage shops and websites such as eBay.com and Etsy.com sometimes list 3-gallon mason jars. FreshPreserving.com sells half-gallon wide-mouth canning jars, which accept the same two-piece wide-mouth lids as Ball’s quart- and pint-sized jars. SpecialtyBottle.com sells half-gallon and 1-gallon jars with single-use one-piece lids. Replacement lids for these jars are available at ULine.com, which also sells half-gallon and one-gallon jars. For fermenting vegetables, kombucha and keffir, Amazon.com lists an Anchor-Hocking 2 1/2-gallon jar with a brushed-aluminum lid and handle.