Rising moons, Alex!
Welcome to the Outer Rim, traveler. At times, the Gatherers have had some scrap pieces available for purchase. Though, I have not seen it as an option on some of my recent voyages to a galaxy far, far away. It never hurts to ask while you are traveling to Batuu. However, to set realistic expectations, I recommend planning your visit to Savi's Workshop with the understanding that only one set of lightsaber pieces is likely to be available per experience. While legacy lightsabers, various accessories, and much more are certain to be available at Dok-Ondar's Den of Antiquities and Droid Depot, individual pieces and sets for custom, handbuilt lightsabers may not be in stock.
That said, it's in the best interest of the Gatherers, and indeed of the whole galaxy, that you have the best experience possible. Should you experience any unexpected defect or trouble with a piece of your custom lightsaber, I recommend requesting an audience with one of the Gathers or a representative to review possible remedies. Or if you have already returned to our galaxy, you may email or call Merchandise Guest Services to seek support. They may very well have connections with the Gatherers to obtain components that may be of use to you.
The wellbeing of the galaxy may very well be at stake, Alex. And you may play a part in it. Besides learning the ways of the Force at Savi's Workshop, another small way you can help may be to seek out and capture some of the scum and villainy who attempt to find refuge in the relatively lawless Outer Rim. If you are up to the challenge, be sure to pack your MagicBand+, load the free Play Disney Parks app on your mobile device, and request an assignment as part of the Star Wars: Batuu Bounty Hunters experience in Star Wars: Galaxy's Edge. The Bounty Hunters Guild set up a self-service kiosk you can visit across the way from Savi's Workshop and Droid Depot.
May the Force be with you, Alex, always!
~Tony