Certainly! Below is a Python function that generates test cases for the "Land Distribution" problem:

```python
import random

def generate_orchard(H, W):
    chars = [' ', '@', '#', '*']
    orchard = []
    for _ in range(H):
        row = ''.join(random.choice(chars) for _ in range(W))
        orchard.append(row)
    return orchard

def tcgen():
    datasets = []
    num_datasets = random.randint(1, 20)
    
    for _ in range(num_datasets):
        H = random.randint(1, 10)
        W = random.randint(1, 10)
        orchard = generate_orchard(H, W)
        dataset = (H, W, orchard)
        datasets.append(dataset)
    
    # Adding the terminating dataset
    datasets.append((0, 0, []))
    
    return datasets

def format_dataset(dataset):
    H, W, orchard = dataset
    if H == 0 and W == 0:
        return "0 0"
    formatted_orchard = "\n".join(orchard)
    return f"{H} {W}\n{formatted_orchard}"

# Example usage
if __name__ == "__main__":
    test_cases = tcgen()
    for dataset in test_cases:
        print(format_dataset(dataset))
        print()
```

Explanation:
1. **generate_orchard()**: Generates a random orchard map with given dimensions H and W, filled with characters representing apples ('@'), oysters ('#'), oranges ('*'), and whitespace (' ').
2. **tcgen()**: Generates multiple datasets, each containing the dimensions H and W, and the corresponding orchard map. The number of datasets is randomly chosen between 1 and 20. The end condition of '0 0' is appended to signify the end of input.
3. **format_dataset()**: This helper function formats a dataset into a string suitable for printing or further processing.

The **Example usage** section demonstrates how to generate and print the test cases. Each dataset is printed in the required format, followed by a blank line for readability.