While the game once had a presence on Steam, it is no longer sold there. You cannot buy it directly, though some users still trade "giftable" copies from their old inventories.
Sega no longer holds the license to sell this specific IP digitally. How to Acquire the Game Legally Download Iron Man PC Game 2008
Currently the most active source for physical DVD-ROMs. Prices generally range from $9.89 to $25.00 depending on whether the game is used (CIB) or factory sealed. While the game once had a presence on