Well, Helium can be found in ANY ballon, if you manage to open one and inhale the air, you'll have the twetty effect, sulfur hexafluoride is a little more hard to find, mostly on surgery rooms and magnesium casting.
remember, both gases are non toxic, but continous inhaling will lead to sufocation death because our lungs don't really breath them.
Helium on wikipedia
en.wikipedia.org/wiki/Helium" onclick="window.open(this.href);return false;
sulfur hexafluoride on wikipedia
en.wikipedia.org/wiki/Sulfur_hexafluoride" onclick="window.open(this.href);return false;
