Platforms like Klook or JRailPass also sell the pass. Note that these typically issue a digital voucher that must be exchanged for a physical pass at a designated JR office in Japan. Pickup and Exchange Process Purchase online - JAPAN RAIL PASS
If you are already in Japan and need a pass, your only option is to purchase it through an online platform. can you buy jr pass in japan
You can buy directly from JAPAN RAIL PASS Reservation . This is the most flexible option because it allows you to book seat reservations online immediately after purchase. Platforms like Klook or JRailPass also sell the pass