The Midgard Fletcher Trainer is in the NW corner of Jordheim. There are three buildings in a row very close to the lathe and forge. The Fletcher Trainer is in the middle building.
The merchants for fletching crafting are in the big building next to the lathe and forge.

You are made to go all the way across Hibernia because, perhaps, Runewood Boards are only grown/made there. These days, capitals, and even large stores have most of the items we need day to day because of international trading. Who does the international trading? Traders, of course. Trading is their trade.. I suppose, then, you could call them Tradeskillers. Now, if all the tradeskillers on X server in Y country went and talked to the tradeskillers in Z country, then perhaps some sort of trade route can be established. Then again, with any established trade route, there comes the opportunity to hold it up. Such is life.

Or, if you want the short answer: The capital doesn't have all the items in it because you havn't established an online corporation dedicated to supplying the capital with hard to find tradeskill components. So, either you do that, or you keep taking your long walks.

Cheers,
-Jhak

Try:
http://www.cannotlinktokills.com/index2.asp

They have tradeskill and material location guides (PDF & Spreadsheets.)

Hope it helps!

13th level thane
pellinor