Bill the guy at the photo shop checked and a 67mm filter will sit in the holder.
A new 67mm filter would be about $40, so he recommended either a used 67mm red or look for something more reasonable in price.
I googled "rubylith" since I heard about it. But it turns out that is a film, not a hard piece of plastic. So it would be tricky to put into the filter holder w/o something to hold it from sagging.