I also love black and white photos.
GMIC has some very nice filters for those.
I hope you do not mind my using one of your images.They are all very nice by the way.
Here is the image of the water shot ran through GMIC>Artistic>Old_Photo.
Here is the same photo with a duplicate on top set at color>invert and _grain-merge mode.
I set the opacity low also. This brings out better saturation in any photo.
Might i also suggest a focus blur? I fear i have done great in justice to your photos with this one. My apologies in advance.