I'm going through the same thing as you, now that I'm plannig on swapping a K24A2.
It seems very difficult to get a straight answer on this subject. As best I can tell after talking to people and reading a whole lot of stuff, the Accord TB and Euro R TB are the only two which will fit the TSX IM.
Off course, I'm sure you could make other things work, but it seems that these two are the only ones requiring no mods. Having said that, I would be surprised if the Euro R TB was not drive by wire. So this leaves us with the USDM 2.4L accord TB which is smaller than the stock TSX TB.
So for simplicity, the accord TB will work, but it won't give you great performance if you do other mods to the motor. I will be looking into getting the USDM Accord TB overbored. I will try and remmeber to post some info on this once I figure it out.
As far the Euro R IM fitting the TSX head, no one has been able to answer that question for me yet.
Pascal