Shalom,

You are asking a well-known question, but there is no definitive answer. The Gemara does not seem to say that the 36 Tzadikim are hidden, but it is possible to say that a real Tzadik tries to stay in the shade, as he is probably modest as well. There is another Gemara in Chulin 92a that mentions 45 Tzadikim -- 30 in Bavel and 15 in Eretz Yisrael. The Gemara asks where in Eretz Yisrael these Tzadikim can be found, and Abaye answers that they are in a synagogue under what he calls the "Yetzi'a." Perhaps this is a source for the idea of them being hidden, since it seems from the Gemara's question that these Tzadikim are not famous, and it is necessary to point out where they are. It could be that the answer, too, does not reveal exactly where the Tzadikim in Eretz Yisrael are. But, in any case, these are 45 Tzadikim and not the 36 mentioned in Sukah and Sanhedrin.

In many Sifrei Chasidus, it is mentioned that the 36 Tzadikim are hidden. This is brought in the name of the Ba'al Shem Tov in many places. The Bnei Yisaschar (Ma'amarei Chodesh Nisan, Ma'amar B, Parshas ha'Chodesh) says that if the generation is not worthy, the great Tzadikim of the time become hidden and may be woodchoppers or similar, because the generation is not worthy to know them. Perhaps this is connected to the idea of the 36 Tzadikim being hidden, too.

I hope this helps a bit,

Aharon Steiner