If you can find a place where the building steel is exposed that would likely make a good earth. Have a look above your suspended ceiling, they often hide a multitude of evils.
Getting some RCD/RCBO protection is a wise move, even if you have an earth. That should mitigate any actual safety issues.
If you are getting tingles off appliances with mains filters then your balcony railing is likely going to be sufficiently earthy to stop them but I wouldn't rely on that as a safety earth.
Using the neutral as earth (connect together before any RCD protection) making the supply TNC-S** would work, but there's always a risk that work upstream (such as a meter change) would result in an accidental L-N swap with predictable results. Unless the system is actually intended to be this way I'd explore all other avenues first.
** Many supplies in the UK are like this, but the N-E connection is in the service-head and so before the meter, getting L-N swapped is very unlikely.