Some restraints are only used in certain places by certain NPCs. Did you ever get pulled into the demon dimension or walk in there in an "Orrery" level?
Could be possible that they are rare, I think I once got an invisible straight jacket that since then I’ve sadly never got again. I don’t know if it’s rare or since then I’m just unlucky
Let's see. Blackhole items IIRC are applied by the demon miniboss accessible from Orrery levels. You may also find them in the shadow chests in the same place. Invisible gag, armbinder, and legbinder are applied by both ghosts and by having a high distraction level while you have the dark desires status effect, gained from either a negative perk, or from being attacked by the demon miniboss mentioned earlier. Shadow restraints (jackets etc) are applied by shadow dragon girls. Crystal cuffs, armbinder, and gag are applied by crystal dragon girls. Divine cuffs and celestial rope bindings are applied by angels and holy constructs. If you piss off the gods faction by breaking orbs and not doing sidequests, they will start spawning as regular enemies. Comfy straitjacket is applied by ghosts and sometimes by the handmaid knights. Living collars you get either by playing with a certain perk and getting jailed, or by reaching the lowest reputation with a goddess. Shadow chains you get by pissing off a goddess as before. Besides the living collar being put on you, shadow ghost thingies will also spawn, and try to bind you with those. Ectoplasmic chains, I think you get by being bound by the wraiths that spawn when you use the maximum level time stopping skills. Ancient restraints you get by looting Ancient Vaults. Those are about all the rare restraints, I think.
