Gummi, a mature tank will have heaps of them crawling round the rocks after lights out.
How old is your tank, and what fish do you have.
Depending on the age of your tank and also the fish that you have, this will have an influence on the amount of pods that you have and will be able to see.
If you are using NSW and introducing live rock into your system, in time you should see them.
And yes you can seed your tank, from fellow reefers and you should also be able to buy some as well.
Good Luck