In windhurst you can magic from places such as the Federal Magic
Reserve in Windhurst Waters, or Kususu's Hoodoos in Port Windhurst. However, the best place to find magic is at the auction house. Often times the AH will have magic scrolls simply not found in the stores. Also, you can get magic scrolls by completing missions such as "Know One's Onions" in Port Windhurst to get scrolls (in this case the scroll of Blaze Spikes). You can also ask around to find out what mobs drop magic scrolls. That way you are getting exp and new spells.
I also believe that the availability of spells in the shops may depend on the nation's conquest status. I have noticed that when a nation is at the bottom of the conquest rankings the shops have far less items than they had when the nation was leading the rankings. This could be another problem to your spell shortage. But in a nutshell the best place for new spells is the auctions house. Make sure to check it periodically to see whats in stock.
In reference to their being a spell for each level, this is not entirely true. I would say that most new levels have a new spell that goes along with it, but not every level. For instance the beginning black mage spells (spell then level): Stone-1, Poison-3, Blind-4, Water-5, Bind-7, Aero-9, Bio-10, and Blaze Spikes-10. As you can see from the above examples black mage levels 2, 6, and 8 do not have new spells to go along with them. However, level 10 has two spells to go along with this level to make up the difference.
Edited, Wed Nov 26 01:37:23 2003 by rdanem