I would suggest you breed like sub species. Keeping a Golden Greek line pure is the best for the animal. Let alone less confusing in the trade as if things about Testudos aren't confusing enough. Though they could breed with other sub species, the eggs are not always fertile. Here is some info on them http://www.chelonia.org/articles/Whatisagolden.htm
I am getting a sense you are in a rush to breed torts? Is there a reason? (being nosy here) I know it may seem hard right now to find another Golden Greek but they will come. Once you do aquire another Greek you should quarenteen them at least 6 months to a year before placing them together for the saftey and health of both torts.