There is a guy selling 'German glass filters', not real well specified, but single-spec choices of '760 nm', '850 nm' and '950 nm, reasonably priced on eBay as Y2KREX.
I chose the 760 as my best guess closest thing to an 87, in 49 mm (front & rear threads) for $9.99 + 3.00 ship.
Sadly, they seem to be marketed to doofusses who put them on camcorders for nerdish voyeurism. Seller communication via eBay is non-existent, but sales rating is excellent. He may not understand all the technical questions I asked about them, or he doesn't bother to read the eBay messages.
Anyway, I got it in reasonable time, in a hard case, with foam case liners stamped with size and wavelength. The filters themselves are unmarked and you have to specify what cutoff you want or you get a random one. I did not get an answer whether the cutoff wavelength is 50% transmission or 0%. I assume 50% and am told by someone else that with IR filters, the attenuation dropoff is pretty steep (but is that log or linear?).
The 760 nm filter (to my eyes), viewing a 60 W light bulb in a sun-illuminated room (open curtains), showed a dim dark red bulb shape. Under better conditions, more (filament?) might be visible. I guess this is a mileage-may-vary scenario, and too subjective to estimate what filter it's equivalent to. He just lumps them all into one group, comparing them to the common photographic IR filters available.
Murray