For lemonade, it is easy to make it yourself. Have unflavored PG or PG/VG mix. To whatever size you want, say 30ml, simply add in about 2% lemon
juice. Yep, just regular old Real Lemon from the grocery store. That would be 0.6ml of juice to 30ml. Some might like it stronger or weaker. Mine has lasted about 4 months, non-refrigerated.