Don't know what make stand you have, but you can probably get the hardware and chain from Loc-On tree stands. Rather than use a chain you should consider using the speed hitch rope Loc-On sells for some of their stands. A lot lighter and extremely quiet compared to a chain. I've used them for years with no problems. Generally replace the rope every 2 - 3 years depending on wear.
You can probably look at the stands on their site and find something close to yours, order the hardware for the stand closest to yours and it will most likely work. It's not rocket science, you can also buy hardware at Home depot, Lowes, Ace, which will be stronger than what is provided by the stand companies. I do this occasionally, but then I believe in overkill when it comes to safety in trees.