In order to get 3" of lift from shackles, you would actually need shackles about 6" longer than stock. That's not really a viable option.
You can reasonably get around 1" - 1.5" from shackles and you can do a 1" body lift without having to worry about effecting much. You would still probably want to remove the front springs to install caster correction shims with the longer shackles.
New springs or doing a spring over axle conversion (more than 3" of lift), are the only real ways to get 3" or more of lift.
You will occasionally find used lift springs for sale as guys part-out rigs or move onto higher, or different, types of lifts. That's how I found mine and it took a year of watching this forum and ebay, but it was a very inexpensive solution.