C&H in South Sioux City, NE might be a good place to start. 
 The 17220 should be fairly common as it was used in a lot trucks. 
 The other one might be a bit harder to find.
 I used a 17220 to replace the rear rear in a DT402 set. Just changed the side gears.
 There are 4 or so on Ebay right now, you would have to check the casting number to determine the series, but it is a good bet at least one or 2 would be a 17220

I am looking for RS17220 and RS23240 two speed differentials.  Does anyone know where I might be able to locate them?  Thank you.