I bought from a local chinese store in Italy.
You can find for about 20$ (I paid a little more, but I didn't have to wait for shipping).
I'm not sure if I can post direct link, but it's very easy to find on the most popular auction site, if you search for usb microscope, for a price between 20 and 35$.
This is very similar to mine, but it is missing light regulation
edit1:
A few more informations:
Microscope came with software and drivers for windows (tested on windows 7 64) and MAC (not tested).
It is also compatible with linux as UVC camera (I didn't capture with commadn line tools, but I'm sure it is compatible):
dmesg output:
[1481783.279425] usb 1-1.3: new high speed USB device using ehci_hcd and address 18
[1481783.390944] usb 1-1.3: New USB device found, idVendor=0ac8, idProduct=3450
[1481783.390947] usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[1481783.390950] usb 1-1.3: Product: Vimicro USB Camera (Altair)
[1481783.390952] usb 1-1.3: Manufacturer: Vimicro
[1481783.391052] usb 1-1.3: configuration #1 chosen from 1 choice
[1481783.436585] Linux video capture interface: v2.00
[1481783.439918] uvcvideo: Found UVC 1.00 device Vimicro USB Camera (Altair) (0ac8:3450)
[1481783.441706] input: Vimicro USB Camera (Altair) as /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.3/1-1.3:1.0/input/input4
[1481783.441809] usbcore: registered new interface driver uvcvideo
[1481783.441813] USB Video Class driver (v0.1.0)
lsusb:
Bus 001 Device 018: ID 0ac8:3450 Z-Star Microelectronics Corp.
edit2:
Chipset is vimicro VC0345