Amazon.com: 256GB SanDisk Ultra UHS-I Class 10 90mb/s MicroSDXC Memory Card works with Samsung Galaxy S8, S8 Plus, S8 Note, S7, S7 Edge, Cell Phones with Everything but Stromboli Memory Card Reader :
Use micro SD card in Galaxy S8 and Galaxy S8+ - Galaxy S8 Guides
Amazon.com: Ubrokeifixit Galaxy S8,S8 Plus Micro SD Card Slot Single Sim Card Tray Holder Replacement for Samsung Galaxy S8 G950/S8+ Plus G955-Black : Cell Phones & Accessories
High Speed Samsung Evo 128GB Memory Card with Case [MicroSD Class 10 MicroSDXC] X8Z for Samsung Galaxy S8 active Tab A 10.1 (2016) Sky S9 Plus, S7 S5, S10e S10 Plus On5
Amazon.com: Professional Ultra SanDisk 64GB Samsung Galaxy S8 MicroSDXC card with CUSTOM Hi-Speed, Lossless Format! Includes Standard SD Adapter. (UHS-1 Class 10 Certified 80MB/s) : Electronics
Amazon.com: Digi-Chip 128GB Micro-SD Memory Card for Samsung Galaxy S8, Samsung Galaxy S8+, S8 Plus Smartphones : Electronics
How to move apps to your SD card on the Galaxy S8 | Android Central