classic motorcycle forum

Hope you can help...my father courted my mother on a matchless g9 500cc twin...and for a golden wedding present we want to buy him one.   I have seen hardly any for sale and when I do they range in price.  New to bikes but do any of you enthusiasts have a view on best place to buy/source (e.g. bike fests, vs mag, vs net, vs auction) one and appropriate price for one in showroom condition??  I have given myself 6-7 months