Extract them from manpage
function tmux__list_options {
local range
case $1 in
-s)
range='/^ {54,8}Available server options/,/^ {54,8}Available session options/p'
;;
-e)
range='/^ {54,8}Available session options/,/^ {54,8}Available window options/p'
;;
-w)
range='/^ {54,8}Available window options/,/^ {54,8}Available pane options/p'
;;
-p)
range='/^ {54,8}Available pane options/,/^[A-Z]/p'
;;
*)
range='/^ {54,8}Available server options/,/^[A-Z]/p'
;;
esac
man -P cat tmux | sed -En "$range" | grep -E --color=never '^ {54,8}[a-z]'
}