Six scraps of cloth are required to craft your own, and they won't even show up as an option without having all materials necessary. You can buy cheap clothes and scrap or salvage them to get the components if there are no shackles available in the market.
there now seems to be another hidden "tech requirement" of some sort. i dont know if it is having research, or having a servant with specific traits, of a specific race, another dungeon room, or a level threshold is the trigger.
at one point, i had ~150 scrap cloth, but only the option to craft bandages. shackles only became available ~2 weeks later. i cannot tell what the actual trigger was, only that at one time i could not craft them, then i could.
shackles wasent the only crafted item this applied to, either. i couldent make lavish meals or exp crystals, either. until like day 60, my available crafting was only demonic brew and bandages, despite having the materials for p much everything else you can craft in the game.