According to the datasheet, it should take the 17051 key.
While I’d normally recommend Beach’s Lock, which is a great place to find fire alarm keys, looks like they don’t sell the key you’re looking for. This ebay listing does, but it’s a little steep.
In the future, I totally recommend Beach’s Lock for all your fire alarm keys. They even sell a set of 11 most commonly used keys for like $30.