The chances of a third movie are exceedingly slim, bare in mind that some people are less keen to entertain ideas of a third movie then others, some people are somewhat realistic, and are resigned to the fate that GB3 will never happen, but if it does, it'll be a nice surpise.
I am also one of these people, so please don't bash people if they don't believe it will happen, also don't try to force people to believe.
And finally, scripts and petitions have been done to death, Sony will not be acceping unsolicited scripts and there have been more GB3 Petitions then I can remember, and so far they've equalled to no real improvement.
So in closing, bare in mind some people won't entertain the possibility anymore, respect that opinion.