Get a lite weight tail wheel.
Mush easier to do as Aden says and get some lightweight parts from Blake at
https://flyboyaccessories.com/
For example, the standard Van's tailwheel tire weighs about 41 ounces... without grease.
The "Deluxe" tire weighs about 32 ounces, and the lightweight tire weighs 25 ounces.
Blake also offers a pneumatic tire. That tire is quite light, but the larger fork might negate a weight savings.
If weight is a real concern, AND you're running a Bell fork, you might consider going to one of Blake's Screaming Eagle forks. At 15 ounces, it is the lightest fork option that he sells. It is roughly identical in weight to a stock Van's fork, but has better obstacle clearance and much better handling qualities.
FWIW, Blake does not sell titanium springs as someone mentioned above. However, we have been considering it. Ping me or Blake offline if you're interested enough to want one. If there's enough interest, we might add them to the queue. They will be more expensive though! Titanium isn't cheap and presents different machining challenges.