Is there any official DVD or ISO of all Amiga modules?
Where can I buy it?

You used to be able to buy the Mods Anthology set (4 CDs) which went up to the 1995-1996 era or so, it's probably online somewhere and has a bunch of stuff direct from the composers.   I don't think there's been another attempt to do something so vast since because it's a ton of work and everything is pretty much online these days.  (modarchive,amp etc.)

I am guessing the best source today is modland at ftp.modland.com/pub/modules/Protracker/ which still seems to be maintained.

yeah modland seems to have almost everything I've ever wanted (ie. everything fleshbrain ever released). The Modizer app is a good way to download from modland and play it on your phone, too, if you're that way inclined!