In a bowl, cover bulgur with 3 cups boiling water. Let stand 45 minutes. Drain well; return to bowl. Meanwhile, cook asparagus in boiling water until bright green and crisp, about 3 minutes. Using a slotted spoon, transfer asparagus to ice water to cool; drain and pat dry. Cut kernels off cobs, and cook in boiling water, 3 minutes; drain and let cool.
Add asparagus, corn, fennel, scallions, and cilantro to bulgur; toss to combine.
In a bowl, whisk lime juice, sour cream, oil, salt, and pepper. Pour over salad; toss. Serve at room temperature, or refrigerate.