@XtherealjaxonX ux used to sell them but the only other way now I believe is through normal sticker shop pack purchases.
You can't get the costumes in normal sticker packs, the only way they are obtainable now is by buying the Torch & Tail upgrade with real world money, it will give you two packs for unlocking hovergoat and torchwood (and some other bonus stuff) and if you open them it will give you a random costume for hovergoat & torchwood because you already have hovergoat and torchwood.
Town hall event starts around the beginning of every month (I believe it can start anywhere from the 4th up to the 9th day of the month), and remains open for 2 weeks each time. Town hall chests also restock each time it reopens again if that's what you are asking, and town hall chests don't give you hovergoat and torchwood costumes.
