LexusRocking,
I've been where you are now and I can tell you that it'll be hit or miss going anywhere but the dealership for a new fob and proper programing. I have researched this issue for quite some time through many forums, and the only sure way to guarantee any fob you buy and program will work 100% is through the dealership. To that end, I have copied part of a previous post of mine on the Lexus ES300 forum of this message board, rather than rewrite it all again.
"Now roll ahead 6 years to my Bride's new ES350, a 2011, which is now push button start, and has a key fob transmitter. She loses the plastic part of the key fob in year two, but still has the emergency key section on her key ring.
A search shows that the key fobs are available online, but even those who take it to a Lexus dealership can't get them programmed correctly in some cases. Some do, some don't.
The result is, buy one online for $100 or so, have the dealership program it for $75 and then maybe find out it won't work, only to have to then buy a new one from Lexus and have it programmed to the tune of $300 or so.
So we just broke down and purchased a new one from Lexus, instead of trying the aftermarket route on the off chance it might work.
So, what I'm saying is that you can get your generation key cut and it will work, but there are no guarantees with the two latest generation ES's."