java moss can be hard to find sometimes, but seems to be one of the most saught after hardly plants. I called 6 stores in my area and found one with some in stock the others said they can't keep it in stock long enough. It grows like a weed though so be prepared to have it everywhere in your tank. But it's a great place for your fry to hide.
If your tank hasn't cycled you have to be very careful and make water changes almost daily. Any ammonia, nitrite is dealy for fish. High levels of nitrate is also very bad. Java moss should help in the cycling stages a bit.
I found a test kit that tested for ammonia, nitrite, nitrate high and low PH. All together is was $29. (CAD) Before I bought that kit I spent way more buying them all individually. During the cycling stage you should test your water at least every other day if not daily. You have to make sure there is NO ammonia or nitrite in your tank otherwise your fish will get sick and or die. I lost many fish before I found out about cycling and biological filtration.