You can usually find it at your LFS, but it will be attached to something else like Java Fern. To be perfectly honest it's really just kind of a dirt magnet and I've been trying to eliminate it from my tank.
If you got your hands on a chunk you could just loosely tie it to your driftwood with some fishing line and it will eventually attach and grow (and collect dirt which will be thrown into your water colum whenever something disturbs it).
You should be able to find it at a local shop. If not, try asking if they'd order some for you (it's easy for them to get).
Personally, I like having java moss in my tanks. It looks nice, and provides shelter and a food source for fry and small fish. Going to add it to the 50g tank I'm currently setting up, as a matter of fact. :wink:
you can use java fern or java moss. I like the moss personally. I just give it a good shake when vacuuming out the tank. I do my tank every 2 weeks. The fry like it for the lil critters that hide in it. personal preference.