Wikipedia says it was only commercially available for NT4, I do somewhere have the Dec Alpha Windows 2000 beta discs (It got killed very late in the beta).
A friend of mine had an Alpha, and I was getting the Windows betas (I got 98se, 2000, and XP, and then nothing else). My friend was really happy to 'borrow' the win2k for alpha discs. IIRC, release candidates 1 and 2 had alpha discs, and then 3 and beyond didn't; but I might be off by one. I assume it would have shipped as part of the release if only Alpha was cancelled a couple months later.
IIRC every RC disk had alpha binaries, only the RTM and later doesn't - because Alpha getting canned was declared in the short window between last RC and RTM, in a rather abrupt manner to everyone involved on the project.
Seems to indicate that the Release Candidate 3 builds for Alpha never made it out through official channels. I'm pretty sure beta and RC was one disc per flavor and architecture though: so x86 professional, x86 server, etc, and alpha pro/server/etc. A big bundle of discs would come from Redmond.
I know nt4 had all the archs on the release disc, but I don't think that was the plan for win2k