Looking for a handle with a keyed lock from outside

Thanks for posting! That should be totally possible. My first thought is to recommend our 82-315, which is designed to mount on top of an existing exterior handle. However I'm not sure if you'll have the room for it, based on the design of your current hardware. You may want to consider purchasing our 82-044 exterior pull to use in addition to the 82-315. In fact, we have a video that shows exactly how these two products interact.