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The Nitro Spark was obtainable in Season 32: "Street Racers" by reaching level 7.
Unlike the other new seasonal cosmetics, Nitro Spark is actually quite often looked for by traders. With most traders being quite happy to take this as a 1M add in trades, or give other 1M cosmetics for it (such as Radiant Ice). This is also way better than other minimal items such as Bloxxer, JDM or BlueS3.
Supply is widely distributed — no single holder owns enough to register as a hoarder.