Brooks are now a theft target, so bear that in mind,

they are expensive even at wholesale to have a small shop stock them

but there are posh shops that will, you have the Googleaire employees, very well paid, to cater to.
and several in the city of SF may have inventory of a couple..
[all can order on demand]

and, being Leather, you have to take care of it so it does not get wet or too dry.

there are probably 1000+ different saddles made..