Spring Trap at Town Hall 18: 9 of them, max level 13. It unlocks at Town Hall 4. Max level per Town Hall, with how many you can build in brackets: TH4 1 (2), TH5 1 (2), TH6 1 (4), TH7 2 (4), TH8 3 (6), TH9 4 (6), TH10 5 (6), TH11 6 (6), TH12 7 (8), TH13 8 (9), TH14 9 (9), TH15 10 (9), TH16 11 (9), TH17 12 (9), TH18 13 (9).
Tap a Town Hall to open this item there. Dashed: not available at that Town Hall yet.