What exactly do you plan on doing with your current stock that is in there? Does the entire tank's current stock consist of a crayfish, bichir, black ghost knife, and peacock eel? And the bichir will be moved to another tank and you plan to keep the crayfish, black ghost knife, and peacock eel?.... Well, I guess you could do something simple like a smaller cichlid such as a JD, or FM.
I personally only plan on having one extra tank besides my large tank, which will be a 55g most likely, and it will be reserved for 1-3 Gulper Catfish, but that won't work for you if you plan on actually keeping any of that stock in the 55g.
Also, limiting yourself to what the lfs has available will just bring you down the road to being bored with the stock you have, just like the current situation you're in. Don't settle for what the lfs has or you'll just repeat this cycle. Get what you want. It's all available online.