A couple of leads to try
1. Larry Barker in Arizona has all kinds of parts; good starting point.
2. Willow Run K-F Parts is another source. The people owning this operation continue to go through what amounts to trailer trucks worth of parts acquired to start the business. They have a good catalog website.
The 1948 Frazer water temperature system is different from the Kaiser system (you probably already know this). For reasons best known to the engineers at Graham-Paige (after World War II) and Kaiser-Frazer (after K-F bought Graham's auto operations in the first quarter of 1947) the Frazer had a sort of one piece thing with a Bordun Tube that fastened into a hole on the engine block casting. The tube reacted electrically to the temperature of the water and caused movement in the temperature gage on the dashboard. The same concept was also used on 1949-51 Frazers, but the dial facing was changed making the two types incompatible.