Probably the best bet would be a replacement, if you can find one. I know that a few collectors have used something called
J-B Weld to fix broken pot metal joints, but I've never used it myself.
You might want to start out by getting in touch with Great Lakes Antique Phonograph --
http://www.victroladoctor.com/ -- which has hundreds if not thousands of parts in stock, and the people there are VERY helpful.
Another shop to check out is the Victrola Repair Service --
http://www.victrolarepairservice.com/Other shops include:
The Antique Phonograph Supply Company --
http://www.antiquephono.com/Shenandoah Antique Phonograph Repair --
http://www.shenandoahrestoration.com/phono.htmlJohn Lewis's Mechanical Antiques Repair --
http://www.antiquephonograph.com/You'll probably need to send some photos and measurements of the tonearm to these places.
Since the phonograph is inoperable at this time--and if you haven't already done this--you might want to have the sound box or reproducer overhauled with fresh rubber gaskets and adjusted. This will greatly improved the sound quality and reduce record wear.
HTH,
Joe