It doesn’t get much more authentic than Avery’s. Its 30-plus flavors of sodas and seltzers (including the hysterical 'Totally Gross' soda range) are still made with 1950s technology in the original red barn where it all started back in 1904. The water is pure well and the sugar is pure cane – no high-fructose corn syrup here.
If your group is at least five strong, be sure to call ahead to arrange a make-your-own-soda tour (price varies). You’ll go upstairs to the Mixing Room and create three bottles of soda to your exact flavor specifications and then watch the conveyor-belt machine downstairs add the water and CO₂ and affix the cap. Sodas are sold by the case (within which you can mix and match flavors), but there are some single bottles available.