You need to scan the normal Link (smash one) amiibo, it always spawns first scan but it gets very unlikely to spawn all the next scans.
Little tip: don't fuck up like I did and spawn epona too far from a stable,
That's exactly what I did lol. Actually, I first spawned Epona before even knowing how horses worked in the game, and that you needed to register in a stable. So I lost her, and was bummed to find out that she's gone for good. Then somebody said that you CAN spawn her again at random, but you have to keep retrying. So.... I was on a beach surrounded by cliffs and water, and for some dumb reason I decided to try and respawn her and it worked!! However, I couldn't get to a stable and was basically stuck riding her around on a beach like a dumbass