I have but it was a Revelation RC fork on my Focus. You need to start with knowing exactly what fork you have (the model , id code is stamped on the fork brace, then Google it to get to the correct page on the Rockshox website).
Then move to the Rockshox spares catalogue, here:
From memory the index is on page 3 and the Revelations start at about page 100.
You can upgrade the damper from the current Motion Control to the Charger damper, you might as well go for the latest version the Charger 2.1. It comes in two sorts the expensive RC and the £100 cheaper RCT3. Don't just go for the most expensive, research what the damper does for you and be honest about your ability (or even desire) to tune your suspension.
If you do not already have a Debonair air spring, you can upgrade that too for about £42, or less if you already have an earlier Debonair version.
The Rockshox tuning guide is very useful, it covers all its fork types and goes into some detail.