to go to meet, to receive, as a guest
迓 centers on the act of going out to meet and welcome someone, especially receiving them as a guest.
迓 combines the movement radical 辶 with 牙, which likely contributes a phonetic element. The character is associated with going to meet or receive someone.
The movement radical 辶 suggests going, and the inner 牙 (tusk, fang) can be imagined as a distinctive marker. Picture walking out to meet a guest carrying an ivory tusk as a welcoming gift.
For ガ, imagine going out to meet a guest and greeting them with a cheerful 'Ga!' as you receive them: Ga -> ガ.