Getting into a Relationship with Whitney might get you in one eventually, if you have "forced crossdresing" enabled.
Or if you're lazy, you can find it in the code, and set a shop to sell it, you'll find a part in the HTML file that looks a bit like this:
Code:
{
index: 7,
name: "flat chastity cage",
name_cap: "Flat Chastity cage",
variable: "flatchastitycage",
integrity: 6000,
integrity_max: 6000,
fabric_strength: 30,
reveal: 1000,
word: "a",
one_piece: 0,
state: "waist",
state_base: "waist",
plural: 1,
colour: 0,
colour_options: ["pink"],
colour_sidebar: 1,
colour_combat: 0,
exposed: 1,
exposed_base: 1,
vagina_exposed: 0,
vagina_exposed_base: 0,
anus_exposed: 1,
anus_exposed_base: 1,
type: ["chastity", "cage", "shrinking"],
anal_shield: null,
set: "genitals",
gender: "m",
cost: 0,
description: "Completely Restrictive.",
shop: [],
accessory: 0,
accessory_colour: 0,
accessory_colour_options: [],
penis_img: 0,
high_img: 0,
cursed: 1,
location: 0,
hideUnderLower: [
"plain panties",
"bikini bottoms",
"lace panties",
"briefs",
"school swimsuit bottom",
"school swim shorts",
"leotard bottom",
"unitard bottom",
"skimpy leotard bottom",
"foreign school swimsuit bottom",
"swimsuit bottom",
"bunny leotard bottom",
"boyshorts",
"catgirl panties",
"G-string",
"microkini bottom",
"highwaisted microkini bottom",
"speedo",
"striped panties",
"thong",
"classic plain panties",
"classic bikini bottoms",
"classic lace panties",
"classic briefs",
"classic school swimsuit bottom",
],
altDamage: "metal",
iconFile: 0,
accIcon: 0,
},
