They are available on Amazon.
I got mine off eBay, same deal. There are many similar
and some lower resolution than you'd like. Here's my
item's listing info (note 12MP camera, a key difference
between the many variants; also, get the ones with
battery):
w/Battery MUSTOOL G1200 12MP 7'' HD Digital Microscope 1-1200X
Zoom C (352978022838)
I went and enhanced mine for what I do; bought
a 1'x1'x1/4" steel plate and drilled / countersunk to
mount the microscope head on a larger magnetic
base, and had the steel place cut me six "pucks"
to which I attached magnets in every-other polarity
to serve as sample and micromanipulator pedestals
(also bringing a thin die up to max zoom range).
The die pic below was taken on this rig, with image
area to spare on a roughly 50x50 mil National LM158
die. Minimum feature 4um or so. This little microscope
is probably adequate for most people. Though for
reverse engineering I always end up back at my
"real" optical microscope with its X-Y stage and an
8MP eyepiece camera, which I scan and stitch images
at higher pixels per micron.
For decent image quality you will want to take delayed
shots to let the mechanical shake from button-press
to damp out.