Where can I find WIN 7 Pro OA MEA I have the activation key?

OA means you can use either 32-Bit or the 64-Bit version,
MEA is I think the European (Middle-east/Europe/Africa) area - which is basically irrelevant.
if you have 4GB of RAM or higher
you can load up with the 64 bit version,
if you have 4GB of RAM or less then use the 32bit version.

A list of Legal and official Windows 7.iso download links
can be found here > http://www.heidoc.net/joomla/technology-science/microsoft/14-windows-7-direct-download-links
a few more (same)
can be found here > http://www.mydigitallife.info/official-windows-7-sp1-iso-from-digital-river/
or download direct from here,

win7 pro sp1 u x64 (64bit) > https://drcdn.blob.core.windows.net/win/X17-59186.iso

win7 pro sp1 u x86 (32bit) > https://drcdn.blob.core.windows.net/win/X17-59463.iso

Digtal River provides these downloads via Microsoft Azure.
Since this is an official download channel,
you can be sure to receive setup files that are virus-free, secure, legitimate and untouched.
Downloading the files from Digital River is absolutely legal and completely free of charge.

To make or create a bootable Windows 7 USB flash drive or DVD to install Windows 7
use the Windows 7 USB/DVD Download Tool (WUDT),
which is also known simply as ISO Tool
which you can get from here > http://download.cnet.com/...72600.html
or here > http://images2.store.microsoft.com/prod/clustera/framework/w7udt/1.0/en-us/Windows7-USB-DVD-tool.exe (direct download from microsoft)

these are retail copys and will probaly have to be activated by telephone.
how to > http://www.sevenforums.com/tutorials/18715-activate-windows-7-phone.html

you will also need to download all the drivers required by
your hardware to function correctly
and save them to a safe place ready for installation after you have
installed windows 7 professional.