How To Get Blocks For The Safari Zone In Soul Silver?

You have to:
A.Get the national dex at the olivine city port from prof.Oak
b.Beat the elite four and the champion
c. Answer a all from the safari zone warden/Baoba  

And he'll call you over and tell you more and tell you how to use them and permision to use them

Ok, I have the nation dex but I still cannot seem to get the blocks, I just did his second task. I beaten the Elite four twice now

Get the national dex from oak at the port in olivine after you've taken down the elite four and their champion. Then a short while after Baobo or the safari zone warden will call you on your pokegear. He'll inform you about blocks and tell you how to use them. When you go talk to him at the safari zone he'll tell you more and allow you to use them. Hope I helped:).

Basically after doin all what was said above, when your in the safari zone, face an empty floor in front of you and press A (or check) and itll say "place object" thats when you can go nuts scattering objects everywhere

You get the blocks after the guy in the safari zone entrance things talks to you about them on the pokegear