try this nordfoto - this link will lead you right to a page with their slide films. Scroll through it and you'll see they both carry 4x5" as well as 9x12"!! Not so hard to find, but being a foreigner, you'll have to buy for a minumim prize of (I recall) 250 euro??? If you can't read German, I can look it up for you on their website. If you're really desperate and you don't want to buy such a large amount, I could try ordering for you through my German relatives....or we could order something together - the Nordfoto people are quite cheap and we need to have new Acros soon.
Hope this helps,