Classic Parts has them listed as part# 74-115. Might be worth a call. Just FYI, the 3600, 3800. And 4100 trucks from 53-59 use the same spindles. There must be some difference in the axles though, 53-55.1 have a different part # for the kingpin.
On another note, have you tried heating things up and forcing some grease in? Before tearing everything apart, it may be worth a try.
