How do I find an item by value in an combobox in C#?

You should see a method on the combo box control for FindStringExact(), which will search the displaymember and return the index of that item if found. If not found will return -1.

//to select the item if found: 
mycombobox.SelectedIndex = mycombobox.FindStringExact("Combo"); 

//to test if the item exists: 
int i = mycombobox.FindStringExact("Combo"); 
if(i >= 0)
{
  //exists
}

You can find it by using the following code.

int index = comboBox1.Items.IndexOf(a);

To get the item itself, write:

comboBox1.Items[index];