There is a feat in, say PH2 or CMage or CArc that lets you reduce the arcane failure of a certain heavyness of armor by a certain amount... and I think there is an alternate class feature (for fighters) in CMage that does something similar
Ooh... snap, I just relooked up the Armored Mage alternate class feature in CMage and it's pretty slick... you really might want to take a look at it.
Oh( #2), Thwyvylyn, yup, that was the feat I was thinking about. I had this thread open and didn't update it before my reply. No... it's not, you have to have the ability to ignore arcane failure to begin with for that feat to work. It was what I was thinking of, but it doesn't work the way I (and you apparently) remembered. It won't really help Tz.
Looks like that Armored Mage class feature is pretty much you're only option.