Easy way to find out if you can buy a specific item, and this applies to just about anything in the game:
1. Is it on the rules page?
If no, it does not exist and you cannot buy it.
If yes, continue to #2.
2. Is it listed as Rare?
If no, see the listing of factions that can produce it, and contact them.
If yes, it is not produceable and you will most likely be unable to find one. If you do, it will usually be unaffordably expensive.