You'll find it in your dreams.....
There's a 25 yard rimfire range round the back of Northfields station but I don't think there's any airgun shot there anymore.
The London Underground club may still have a range at Hanger Lane station but, again, it's rimfire.
Indoor airgun ranges of that distance simply don't exist in that area (unless there's something I don't know about).
I don't think the Ham & Petersham club's indoor ranges are that long and it's too formal there to welcome casual visitors.
Err, Bisley?