Chris, I am thinking to sourcing mine via
http://tan14.com/gears.htm in HK. I contacted Them after seeing a link to the site on this forum. They have the ACF filter your after listed. They can also source used cameras and mod them for you if need be.
The charge for modification is only 40AUD, this is the best price i have seen around.
And the estimates on used camera body's is about the same as i have seen for on US sites for used equipment, if not a little better.
If I had your skill i would mod the camera myself but i rather get a working camera than fried chips.
There is also DSLRAstro in the UK who have very similar pricing and offer the similar mods. The currently have the 400D modded for about 500GBP which is around 1000$. Not sure if this is a used camera or brand new.
Regards
Fahim