Other reefers are the best place to be honest... best prices, healthiest specimens (generally)... but depending on the type of 'nem, you can find them out at the LFSs around here.
i normally get mine from Sho Tanks in Mundelein, Illinois. I always get nice and healthy nems from them and you can also get some from fellow reefers also
If you are looking for a BTA then I would suggest other reefers (better prices and you know the nem has already adjusted to captivity). All other nems you are probably going to have to hit up a LFS. How long has your tank been up and running?
I dont know if she is selling anymore to the public right now but I got one from Mrs. Booyah (Booyah's wife lol) that is probably the most beautiful anemone I have ever seen in my life. Got to see her grow out area and she really takes care of them. If you want to see a picture check out my build in my signature, its the first picture on the first page.