I'll add that either Antique or Angela Instruments have boxes galore.
Also, Antique and other have a egg-crate type dividers especially for
various tube sizes.

I have bought a few of the big flat egg-crate boxes from AES, and they work
fine.

If you have small glass miniature tubes, I found a cheapo solution by
accident last winter. The local hardware store sells replacement C-9
Christmas bulbs both in small 25-bulb egg-crate boxes (some of which I
bought to replace the previous year's burned-out outdoor lights) and loose
in bulk bins.

I found that the leftover bulb boxes were perfect for storing loose
miniature tubes. The mini tubes fit right in. Metal octal tubes fit OK if
you store them upside down, so the projecting base clears the divider.

I suspect that this store receives all of those bulbs in the same 25-bulb
boxes and then empties some into the bins for people who only want to buy a
few. Which means they probably crush a few hundred of those nifty little
boxes in the months leading up to Christmas.

Costs nothing to ask. If you volunteer to stop by on the nights when they
stock the bins, and carry away all that pesky cardboard, you might come home
with a bunch of free storage boxes, and even save a piece of a tree!

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html