Kenwood's 455KHz filters were made by NDK.
There are a couple of variants - the YG-455C has a 455.0KHz center frequency, while the -C1's is 455.7KHz. Thus, they cannot be interchanged without retuning the BFO a bit.
JRC "CFL-" crystal filters, on the other hand (also made by NDK) will directly interchange with the 455.0KHz Kenwood units. In an act of unholy matrimony, several of my NRD-5x5 receivers have Kenwood CW filters installed - either 500 or 250Hz B/W. I also have a YG-455C in one of my JST-135 transceivers.
Inrad made 455KHz filters for the early Kenwoods and for JRC gear. I occasionally see these come up for sale used or on the auction site, and Inrad still carries a few models (albeit $pendy).
So you have options.