Björn, thanks! The IR filter is made by Fujifilm. I'm not sure if it is sold outside Japan. Bob (bobfriedman) bought some when he came to Tokyo.
Fujifilm has been producing various square (75x75 or 100x100mm) color correction, sharp cut, special band-pass, ND and IR filters since the film days. They are made of tri acetyl cellulose which is much more durable than Kodak Wratten ones made of gelatine.
You can select the IR filters of various cut-off wavelength by 20nm step. These filters are very handy for the experiments. I cut a tiny piece from the 75x75mm sheet of IR84 filter and taped it onto the lens of the cellphone camera.
The image is SOOC jpeg from the cellphone.