Beautiful radio! Sorry I don't know what driver it used but likely it was made by another manufacturer - and that could have possibly changed a few times during the production run. That it is "slip-on" rather than threaded narrows the field some. I see the occasional driver at swap meets. You might try placing an ad in Antique Radio Classified - http://www.antiqueradio.com - (or better yet, send them an article about your radio with pictures and state in the article that the driver is missing - this will get more attention than an ad). Also contact Playthings of the Past (http://www.oldradioparts.com) - he often has hard to find parts...
:I recently bought a LanSing W radio (United Engine Co.,Lansing, Mich., probably made by Wilcox Laboratories, Charlotte, Mich.)
:Unfortunately the driver of the internal horn speaker is missing. Does anyone know what it looks like, or where I could find it?
:http://www.vintageradio.nl/Radio's/lansing_w_engels.htm
If I was going to use the radio on a regular basis, I might use a small coupling transformer wired to a small 2 inch speaker of good quality, with a rubber surround. The speaker would be glued to an appropriately fitting circular wooden board of the same diameter as the speaker. A hole in the middle would allow attachment to the radio's horn speaker. The small moving cone speaker with the rubber edge might give you better sound quality. It certainly wouldn't look original to anyone inspecting the inside of the radio, but it might be easier on your ears for normal listening.
T.