Search for the ones you want, or find a large list here.
Play-Asia has somehow come up with yet another supply of rare and discontinued amiibo, and most of them are going for a meager $16! We don’t know how long this will last, so if you intend on picking up many of the reruns of the Smash 4 amiibo set once Ultimate releases, this is a great way to make sure you get them. Take note: the ones that are listed as Pre-Order are going to come out January 2019. The amiibo listed as Summer Sale can ship within 24 hours, and most of the unmarked ones ship within a week.
If the character you want isn’t available, you can use this (somewhat outdated) list to see what alternatives there are.