My PC is a very high level Kensai/Mage and he can finally cast the highest level of spells. Unfortunately, I can't seem to find any :(. If you know where some of these high level spell scrolls are or if you happen accross any, please respond with the location (the type would be nice too) ;).

Thanks in advance,

Immoral

At the adventurer mart, the guy propose me to see his special inventory (for a 50 gp fee). There is rare spells and I think that he had some high level spells.

Try this

Sorry. The Pramenade was the first place I went. Let me tell everybody where I've looked. Athkatla (every town), Trademeet, Umar Hills, Windspear Hills and I'm now sailing to spellhold Island (can't remember the name).

Immoral

The AMart's special items will be available when you get back from the assylum.

There's a slew of 7th level spells available at the Copper Coronet. (Scroll all the way down the merchant's inventory). He also has one or two 8 and 9th level ones.
Another big stash of scrolls is on a lady at the far end of the Adventurer's Mart. She's unlicensed and illegit but has a bunch of high level spells for sale...
Ranging from 7-9th level I believe.