Considering we don't get arrest wands, I think it would make sense to allow the Muster access to shackles at a cheaper than normal rate so we have some way to keep arrested PCs under control. Or even to have them in at the same price as Tinker Tom, it's odd we don't have any for a guard faction.
Sergeants got arrest wands, but they never worked right.
Try subduing them multiple times until they move at a snails pace. It's crude, effective and suits a tiny minuscule backwater village's methods quite well.
It also lowers their AC to 0! Guaranteeing instant death if they try anything.
A subdued PC should be cooperative, even if healed!
Think of it this way - if another player subdues you instead of FDing you, they've done you an immense favor in that they're trusting you to cooperate with the situation without the need to strongly penalize you.
If you don't cooperate (multiple times, I'd say. a warning re-subdue is sporting), then you really leave the person no choice. Unless it's simply a new player who doesn't know what's going on, I think a player who consistently tries to escape subdual capture without being somehow rescued or freed invites FD.
I'm not suggesting this as a result of any particular OOC issues with bad attitude, so it's clear. Any time I've had to arrest a PC, it's worked fine. I'm suggesting it because shackles are a cool item that doesn't see much use. It came to me when we'd captured Dreggs and Eldorig, someone suggested IC about clapping them in irons but nobody could work out where to find some shackles.
Honestly, the Muster doesn't strike me as a enforce the law type of group. They can, but isn't it more of a bunch of commoners willing to defend the place? If you character is so inclined to use shackles, buy a pair. I doubt mistlocke really has the income to give out these types of items to their men--even discounted.
It is a VERY WEAK militia.
AKA: Have such little power
Also, what I forgot to mention is that Shackles have a use in limiting PCs without subduing them and needing a DM, or even as a precaution for if you don't reckon you can sub a PC normally if they later resist. Mistlocke's a backwater yes, which is why every Musterman can't automagically zap PCs into the cells like the Watch or Stygians could. Shackles are the cruder option and the Muster would still have to pay for them out their own pocket, even if they were discounted. Clearly the Sgt's arrest wand represents something like shackles anyway, and I can't see what the huge drawback would be in adding them to the shop. It's a 5 minute job to alter a store.
If you've played a Muster PC you'll know that the Quartermaster does sell a selection of basic but useful equipment and potions at slightly cheaper than usual prices. They might not have the funds to give everyone full kit, but they can at least offer some stuff. I'd consider Shackles to fall into this, and 500 gold for a rarely-used item at the market merchant isn't an encouragement to use them ever.
I suppose the thrust of the argument is this: "What is the point in having this item available when PCs that could make interesting IC use of it don't because either it's not cost effective or they can't find a set?". We've got a whole set of systems based around shackles. Keys you can steal to free someone or yourself. Lockpick tools a skilled PC could use to bust themselves out. However they never see use.
This should be pursued in-game and is very possible to be added.
Though shackles aren't cheap, they're not exacly unaffordable either. Your average PC spends way more on potions and wands.
If you think the use of shackles is so vital to the functioning of your Muster PC, just go and buy them at the going rate.