If you know someone who grows, ask them for a few clones. If you don't have access to clones you will have to get seeds. If you don't already have some, you can ask you friends to save you seeds out of any good weed they may come across.
The better the weed that the seeds come from is, the better your crop will be. If the weed the seeds came from was no good, your crop will probably not be any better.
If you need seeds, you can get some online. You can search on one of the search engines listed here. Use the term marijuana seeds or something similar.
Try to find someone that ships their marijuana seeds from the country you live in. That way, your package does not cross international borders and is less likely to be searched.
When buying seeds, don't get the overpriced, exotic ones. Look for moderately priced, hardy ones like skunk. For a descriptions of marijuana strains click here.