Where to find a lid for my fish tank?

I know that I am probably stating the obvious, but have you tried your local PetSmart or PetCo? Those two have always had my 100 gallon aquarium parts. I have also tried my local (small local owned) pet store, they carry more specialty parts but you might have better luck at yours...I am sure you have an unknown in some part of your city, you could try, look in the phone book or google Pet store or even feed store in your city. Also try Amazon or Overstock, sounds weird but those two have almost everything. Good luck!