You can get GWX3 (and probably 2, if you're so inclined) from Jimbuna's Filefront page:
http://www.filefront.com/user/JimbunaGWX2/
For 3 you need the GWX3.exe file and all seven GWX3 .bin files. Download them all to the same folder on your hard drive, then run the .exe file to install. Must be installed over a fresh, new, unmodded SH3 v1.4.
You can use Anvart's mod here:
http://www.subsim.com/radioroom/showthread.php?t=165617
to get a flag plus some other eye candy for your u-boat. Don't know if it works with anything but GWX3 though.