The problem is, you can't program a new key without an existing key. You would have to buy a new ECU which is well over 1,000 bucks. You need to call Customer Service at 1-800-25-LEXUS and tell them you lost all of your keys and they will pay for the ECU provided it is your first time. You have to agree to pay for two keys and labor.
Why are so many people in this thread talking about making new keys? From just the thread title it's obvious the guy needs a remote, and when you read the OP it's obvious he has the key and just needs the remote. Why would he care about the cost of or where to get a new key from.