Or you could try and pick up a Black Country cob type saddle second hand.
That is what I did. Mine has a flat back but a wither as well, and I was lucky enough to find a secondhand Black Country cob WH saddle on ebay. Seller was an absolute diamond, taking measurements, digging out pics of her horses back when he was in work (he was retired and her new horse didn't fit the saddle), and with the enormous help of Poohsmate on here, between everyone the saddle was pretty much the perfect fit!
Poohsmate reflocked it, and about three months ago he came back to flock it again because Tobes had slimmed down.
Love that saddle and it fits him beautifully. And only cost £230!