Hell....that dam battery IIRC its a 2026 can be found in just about any decent gas station, candy store, coffee shop, Staples, Office Depot, Camera store, Shop-Rite, Path-Mark, A&P, and the list goes on and on.
I replace the battery when it starts to fail to work every so often. Usually every year or so. The thing is though by now....if your into your bikes enough to be hanging around on a HD forum, you should have dam well set your security code to a easy to remember personal number. That is one of the first things I do when I get a new (or used) bike....right after I remove all the stupid decals, and reflectors. I know in most cases the default code is either the last 5 of the VIN, or could be 11111. But if you have a factory service manual, it will tell you in step by step directions my 3 year old daughter could follow in her sleep, exactly how to reset the code even if you dont have the existing code.

 

Program your personal code in and carry it in your billfold with the wallet card. I have seen what happens when someone looses their key fob and the alarm is set. I have also had a key fob myself die and the battery didn't fix it.