Fast travel into Scorpion Gulch and find the wastelander who is either already dead or about to get attacked by Bark Scorpions. If he is alive wait until the scorpions have killed him and then search the body for a 'Sunset Sarsaprilla Star Bottle Cap'. Fast travel to Novac and wait three days, then fast travel back to Scorpion Gulch and repeat the process. The wastelander will always have a star cap on him whether he is alive or dead and you can keep repeating the process until you have gained the 50 caps which are needed for the 'The Legend of the Star' side quest.