Are you sure that this is a Q21R? Is it yellow?
The reason that I ask is that I've owned one and one thing I remember clearly is that the Quadra 21R had a stack of 6 small elastomers that the rider could swap out to "fine tune" the ride, instead of one long one. The Quadra 10 (gray) had one long elastomer.
Anyway... There was no way that I've ever remembered to swap out the internals to increase travel length. However, if you find parts from a long-travel Indy SL you may be able to swap out the stantion/steerer assembly and use the internals from that fork while keeping the lowers from yours.
Good luck!