Hi Barry,
So how often do you expect the inputs to change state? Thosands of times per second, once every week or perhaps somewhere in between?
Do you need to detect BOTH edges of the signal or is either the rising or falling edge?
Are the inputs asynchronous in nature or do they change "in sync" with each other?

I'm asking because perhaps it can be done without interrupts, if a suitable chip isn't available.

Another option to look into is one of the "port expander chips". I've never used them but I think some of them have IOC capabillity but then again it depends on the timing requirements etc.

/Henrik.