「定員に達したからワーホリビザが取れなかった」みたいなことが言いたいんですが、quota　has filled とかover the quota　とかって言えるんでしょうか？？何て言えばいいの？？

visa cap (limit) for 2006 has already been reached　・・・などといえば通じると思いますよ。 　

You need to find out the dates for getting ’Working Holiday Visa’ application forms for 2007; earliest date for applying for 2007 and get all the details ready. My friend did that in Kochi in 2000. She got to Vancouver with no trouble in 2001. Another friend applied to several countries in 1998; in 1999 she went to New Zealand; later she applied to Australia because she had enjoyed it so much.

I would apply to all the countries that have a working holiday agreement with Japan and see how your luck turns out. I think that a lot of the details are online ?