Hello chaps, thanks a lot!
I've found a great parts shop on ebay US today thanks to this ref number.
but I've also found the Nikon Netherland Service webshop. they had the parts in stock (luckily). :D
btw Niko I'm a japanese living in Belgium. If I lived in Japan I guess it would have been waaaaaaay easier to find all this (lots of nerds lol).
If anybody's looking for D300 parts I have now a few good addresses, just ask ;-)

+1 with jonny since you already have the part number it should be easy to get it straight from Nikon parts dept (assuming that's the right part#). Though since you live in Nihon you'll have to call the part dept there instead.

Maybe even Adorama has it, try calling em, heard from a friend they have lotsa small litle gizmos you wouldnt expect them to have, including those i reckon.

I don't know where you are, optima, but NikonUSA's parts department should have it, probably for a few dollars or so:
Phone: 1-310-414-8107
Fax: 1-310-322-6979
7am – 3pm PST Mon – Fri

Yup, right. It's not free. On the other hand, I already looked everywhere and even on Ebay it's difficult to find.
I even wonder if these aren't subject to NDA in Japan. I guess Nikon doesn't want these manuals to be freely distributed on the web...
For a bizarre reason, I was able to download service manuals and parts lists for 37 Nikon lenses/cameras but in my download history they only recorded 7 downloads (whis seems to be the maximum allowed per daily "gold" download fee (8$).
I don't regret at all, it's really interesting to analyze all the lenses service manuals, how they're built, how they work, what's behind those caps, how scary it is to move the VR units, each modern lens need specific tools to dismantle, how and why lens alignment analyzers are needed, etc. The old "archive" lens parts lists drawings are really amazing, with all the precise notes for the small tolerances needed to adjust the correct optical properties. Could make great posters!

Dang. They charge your for downloads! Nice site, but not worth my money.

do you know this incredible site?
http://www.nodevice.com/manual/nikon.html
I was looking for the usb/hdmi rubber door replacement for my d300, because it is so deformed now that it doesn't fit anymore, and therefore exposing the interfaces to the elements (rain snow dust). I was looking for service manuals and retail parts websites when I stumbled upon this site... actually I discovered a real treasure for people interested in repairing nikkor lenses and cameras (=geeks like me) :^D
I already downloaded d300 service manual and am ready to replace that damn rubber door/hatch (ref parts 1K660-330 aka IF LID) but I can't find it yet.
what I love in these service manuals are those expert tricks to inspect the cameras/lenses, the special tools, the inspection standard methods, etc. everything is well described and it's very interesting but to go beyond simple things you need special nikon tools and a good knowledge in electronics (not to mention leadfree soldering irons, etc.)

Does anyone have a good website where I could find that part?