What guitar and tuning machines are you using? Some may require drilling, and short of gotoh carbon fiber I don't think you'll find many that will be much lighter than simply removing the gear cover off your existing ones. Or swapping the buttons for plastic/wood. They're out there, but you're probably looking at grams of total weight savings for $$$. Kluson prestige maybe for 3+3 and Hipshot open gear for inline might be the less expensive variants available. Perhaps someone knows other sets off the top of their head, though.