Pentax 6x7 - Chimney Finder Eyecup?

So I just bought one off of eBay for a steal but noticed it doesn't have the rubber eyecup. Does anyone know if I can grab any old rubber eyecup off eBay and if it slides on? Or was it mounted within the eyepiece itself in a specific way? I can't find any detailed photos about this.

Any help would be greatly appreciated.

Thanks!

--edit

I just did some image searching and it looks to be sandwiched between two pieces so buying a rubber eyecup may not work... bummer.

I use a similar chimney on the rb67. the eye cups are not easy to find but what I did was find a rubber lens hood with the same diameter of the mount of the chimney. I take the rubber hood off the plastic threaded piece n crazy glue it onto the chimney mount.