Where can I find this ?!?
 

I was thinking of building some new dirt jumps where no one can come and destroy them like those we had last week... Where should I find the material? Should I bring my friends and we dig a huge hole and take earth? Or Is there possibilities to make the Municipality bring 3-4 trucks full of earths for us ... (I don't think so)?
Please help me ...

Both. Go find a trail that leads into an opening and get dirt from far off of the trail. Wheelbarrows are great if you can get them there. Use rocks and logs in the dirt if you want. Sometimes municipalities will bring in truck loads of dirt, they did for my friend travis. He got a huge amount of dirt for free.