You could buy on Yahoo Japan through a proxy bidding service, but the descriptions (and translations) are woeful and you really take pot luck. I have had good and bad experience with this.
You are correct in that the GL690 seems to have a more sturdy film advance mechanism, and slightly better viewfinder.
You are unlikely to get one in 'excellent condition', as cameras of this age will require a CLA on a regular basis, but once this is done you have a winning set-up, particularly for portrait and landscape on the tripod. Just get a good digital meter.
Good luck and bag yourself a rare classic.
You'll also need a good lens hood.
