Previous gurus or teachers of the Buddha When Gautama left his palace to become an ascetic, it is said that he found some Gurus he learnt from, and left further dissatisfied. Is there any mention of that period of the Buddha's life in the texts? Or did Buddha speak about these experiences? 

I got this link : http://www.buddhanet.net/e-learning/buddhism/lifebuddha/13lbud.htm
This is found in the Ariya Pariyesanā Sutta, (Deva) Saṅgarava Sutta, Mahā Saccaka Sutta, etc.