Looking for some stones

[lucars]

Hello,

I have Malawi fish tank, and I have plan to change decoration.
Where can I find some nice stones to build up some nice cave in the middle (because it is bought sides aquarium).
I thought about white sand and lava stones in the middle, what you can recommend? And where to find best lava stones?
All kind of advice's will be great.
Aquarium has around 600l.

[Sibbi]

Stones you can find in Rauðhólar

http://en.wikipedia.org/wiki/Rau%C3%B0h%C3%B3lar