I've been banging my head on this one for a while. Usually when I need parts I have to email my local International dealer with my VIN, wait for them to try to find what I'm looking for, get me a quote (that's usually ridiculously marked up) then go look online for interchange part numbers, then finally do my online shopping to find what I want.
Then tonight, I found this:
https://repairlinkshop.com/HeavyDuty...rtlist/split/0
Just register, select a dealer (can be anyone whether you use them or not)
Once logged in, create a "cart name" - can be anything - then click the Open Catalog button

Then, boom, you're in Oncommand. See your build sheet, look for parts, whatever.
I hope this helps someone else out there too!