I don't see a way to left align the placeholder text, but part of what you are looking for might be achieved by setting the search bar style:
searchBar.SearchBarStyle = UISearchBarStyle.Minimal;

Otherwise you will have to not use the built in search bar but create your own view. See: https://stackoverflow.com/a/20384021/2913599
where the accepted answer is: "Don't use a UISearchBar if you need to do these kinds of customizations. You'll have to make your own using a UITextField and a UIImageView, and responding to the delegate calls."
However that thread has some other ideas about aligning the placeholder text to the left. The only one I could get to work was to add space padding to the placeholder text, e.g.:
searchBar.Placeholder = "Search ";
How many spaces you need to pad with of course depends in the search bar width. With the added space padding I got this:
