May need to rehome kitty per landlord

I really don't know what to do here. I moved into my apartment a year ago; they said declawed cats are fine with a $300 deposit. Shortly after I adopted Penny but I did not pay the deposit. I was planning on it, but life got in the way.
Then two months ago I adopted Oliver, who was 4 months. The only reason I got a second cat was because I was worried Penny was bored and lonely.
Now, I received a letter from my landlord saying I must vacate or get rid of one cat; apparently tenants are only allowed to have ONE cat. (This also means someone must have seen the kitties in a window and snitched on me. Why???) I didn't know this, otherwise I wouldn't have gotten Oliver.
Oliver is awesome and could get along with anyone. Penny on the other hand, is skittish and shy. I love my apartment and have only been here for a year. I also love my kittens dearly and it breaks my heart thinking of not having one or the other in my life. Also, I don't have a lot of money for security deposits and pet deposits. I'm really at a loss and don't know what to do.

You did say you have not paid ANY pet fee yet, but youhave two cats.  Landlords always find out eventually so it is best to either follow existing rules or make special deals (in writing) with the landlord to make your case an exception (i.e. you may have 2 cats and will pay X-amount of pet fee.)  If he does not agree, it were me, I would move. Also, if the cats have not been declawed, definitely don't do that to them!!!  Search this site for the many reasons why not.  

If you would rather rehome Oliver, try networking with your friends and see if someone would take him either temporarily (until you find a new place to live) or permanently.  I'm not sure where you live, but in some areas it is now against the law for a landlord require that cats be declawed in order to live there, or that dogs be debarked.  Check the laws where you live.