Wish to replace with lock & key on one outer handle, second handle would be dummy.

See our 82-030 Handle Set. The outside pull can be adapted to use our 82-310 Key Lock--see this blog article here for the details. We don't sell dummy handle sets, but you might be able to use a second 82-030 to do the job. If you need a mortise lock and keeper, see if the 82-265 and 82-249 match up.