Looks like some sort of syno's to me. They are pretty available but I am unsure if the breed you have is rare, if you found it at a lfs probably not, but you never know. Nevertheless, very nice fish
I recon by the looks of things you're right smithrc, baby decorus. There are a few of them about in the shops I have been in lately. I think the last ones i saw were about £7?
I have one of these that is about 6" now and I bought mine when he was the size of yours. Make sure you have a large enough tank for them, because they are very territorial of their holes.