Are they attached to nay sort of base? If not you may need to find a small piece of rock and secure the shroom to it. I like to use a rubberband and bridal netting, but there are many options out there. If you warp the shroom make sure it isn't too tight or the shroom will split.
As for picking out corals I have mostly purchased frgas both at LFS and on-line. I did buy a larger coral from this site and it is outgrowing my small tank quickly, BUT I think it can be inspiring to start with one larger piece and then add frags from then on so that things take on a reef look more quickly. What size is your tanK?