Last time I decorated an mbuna tank I actualy didn't use rocks
I decided to try something different and pretty much 'sculpted' a series of rocky structures (including caves and such) out of (white) clay. I then got someone I know to put it all into a kiln for me and (I think the term is) fire it. I ended up with a rather surprisingly natural-looking set of 3 clay rock/cave ornament things
The main benefit to all this was that it was a cheap thing to do (the clay also came from the friend for free I don't know how much it would cost otherwise), rewarding because I'd made it myself and somewhat more practical than rocks because there's no danger of colapse and you can mould everything to your liking. I actualy got the inspiration from some pictures I saw of someone else's tank (not on this forum). I tried to find them but they appear to have vanished
Having said that, something like that is probably not to everyone's taste... So, I have used (annoyingly expensive) slate from my LFS to decorate my tanks but I've also (often against my better judgement
) used rocks I've found in the countryside or in/around rivers. I haven't ever done this with mbuna so I always used the 'acid test' to check whether they'll raise my pH - but with mbuna this isn't a worry. The main thing is to clean/boil the rocks to ensure they don't contain anything harmful and to make shure you collect rocks from places where they are unlikely to come into contact with any dangerous chemicals. There's an article in our FAQ about rocks:
http/www.fishforums.net/index.php?showtopic=55806 You may want to browse the member's pics section as well and check out any african cichlid tanks that have beenposted - someone inevitably asks what kind of rock the person used
As for buying fish online, I can't be any help there unfortunately... I've always just got my LFSs to order things in for me if I've wanted something particular and I've never needed to order mbuna as the species I've kept and realy like are quite common anyway. In fact, you should be able to find the labs at your LFS and chances are you'll also find acei (though maybe not the variant you're after) and socolofi if you browse around FSs.