This may be a long shot, but you could try finding some aftermarket bushes.
Bushes for Impreza/Legacy etc.
http://www.powerflex.co.uk
http://www.superflex.co.uk
http://www.noltecsuspension.com
Generic Bushes
http://www.antivibrationmethodsrubbe...er_bushes.html
http://www.gmt.gb.com/gmt-productrange.html
I had a similar problem with our Justy, trying to get a bush that Subaru didn't make anymore.
I found a generic rubber bush manufacturer who had something similar. They sent me a free sample which I planned to machine slightly to fit.
But then I got an email from a guy in Belgium who had exactly the right bushes. It turns out that the bush used on the Justy is also used by Volkswagen.
Phil.