Bintel and Andrews Communications both sell GSO dobs with warranty, Bintel under their own brand.
https://www.bintelshop.com.au/welcome.htm
http://www.andrewscom.com.au/site-section-10.htm
Both are good to deal with as far as i understand.
I had the Bintel 12" dob before upgrading and wheeled it out of my shed on a trolley for each session. No Problems. It is a bit of a handful if you're going to transport it by car a lot. Quite possible, depending on your car and your preparedness to lift 20kg or whatever the OTA is. I had no problem with this and it was fine in my Camry wagon. Other people find the 10" more portable and you don't lose a lot in light gathering power (about 30%)