The internals of each post are unique to each maker, so your only hope of getting replacement parts is to contact the maker. Ask for both parts of the keyway system that keeps the top and bottom aligned.
If it came on a bike, and the bike isn't too old, you might also contact the bike company and ask about repair or replacement. Odds are you will not get the parts, but you might get a new post free if you ask nicely. Otherwise buy a replacement post with or without suspension as you prefer.
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