>>7908198There are two main ways to purchase specific Lego pieces: directly from Lego, or through Bricklink (which was recently purchased by Lego).
https://anon.cafe/lego/res/21.html#q152This link shows you all the pieces that are currently available to purchase in bulk directly from Lego, so you can use it to easily plan out an order. Ordering directly from Lego is the easiest option, but the tradeoff is that you can only buy pieces that are currently in production.
Bricklink is the main marketplace for out-of-production pieces, but the tradeoff is that you can only buy as many as the individual seller has in stock at the moment.
