Beneficial bacteria

[Mabed]

Hello;
I am starting a new 55g tank and would like to get some used filter media to help with the cycling process.

So far I cycled the tank for 3 weeks but after introducing some fish (10 fish over 10 day span) my amonia and nitrite levels are not stabilizing.

I read that using filter pads or filter media from a cycled tank will help significantly. Is this true? And where do I get this?

Can you guys help..
thanks