Here is a sensible answer, after my offer of early 1960s Multigrade filters - Yesterday the Photo Warehouse catalogue arrived from Ultrafine Online (eBay seller ultrafineonline 12729)

In this are offered three sizes of multigrade filters fairly cheaply, 'though the original manufacturer is of course not stated - I have now made two purchases from this company and both have been good - Unfortunately I put the catalogue on my office desk, so there is no chance of finding it again