[Coco] NitrOS-9 beginner

[Robert Hermanek]

I still have not had the time to learn how to even boot OS-9.

Posts here indicate that at this point in the game, it would be better 
to use NitrOS-9 instead of some kind of vintage OS-9 L2 disks.

I have the "Complete Rainbow Guide to OS-9 Level II" sitting here and I 
have an idea of stepping through the books nice and slow and perhaps 
learning something.

That being said:  I am confused by how/where to get "standard" or 
"un-customized" disk images.  Also, I find there are 40 track disks, but 
I do not have a 40-track capable system.

So:  Assuming I have the rainbow guide in my hand, a 512K coco 3 with a 
single 35 track drive, and a free hour on the weekend, how should I 
proceed?  Does someone keep "reference" .DSK image(s) for OS-9?  If so, 
and again assuming they are 35 track, I could take .DSK files, and get 
them restored onto real floppies via HDB-DOS and drivewire with little 
trouble.  I guess I just don't know which .DSK image to start with...

Thanks
-RobertH