Barry, I have been sporadically looking for secondhand ones from Hoya, which are not cheap, these look quite interesting and the price is right, around $26.00 AUD delivered.
Might have to see if I can allocate some time resources to that. Currently outfitting a new camping vehicle, which takes time, effort and money. This is the priority at the moment, but come spring, I feel that I may get one of those 67mm filters.
Hoya only made their IR filters around every 18 months or so, and then they only did certain sizes each manufacturing run. I waited nearly 2 years to get my 52mm IR filter. That was around 35 years ago, things sure have changed.
Better check on my bellows for IR, not sure if they can handle it.
Many thanks, Mick.