Suggest you ask peeps on the BD forum - they would propably know a bit more the only place I know is Patey (Cirencester and London) although Shires did have one in their catalogue but can't vouch for it ! If not send Piggy / Emily a message via their facebook pages - worth a try !!
I bought my antique one that I use for side saddle at a vintage clothing fair. It's in mint on condition, was only £55 and still has it's original Edwardian box! It may be worth trawling antique fairs, vintage clothing fairs, etc to see if you can find one as then you can try it on and try to bargain down the price.