Here's another one:
Get a bunch of stickers that have your company name/contact info on them, along with "This keyboard is warranted for life".
Give them out to smaller businesses (those that wouldn't likely have a full-time IT type).
Now you've got your name and number in front of them all the time. IF someone does call you on the free keyboard, your bound to find other things wrong ....
(I got this from an HVAC friend who's doing the same, but with thermostats).