Forum user diver Dave repairs waders and the like and he also sells spray on waterproofing suitable for a range of clothing etc.
as some might recall I'm a big fan of the British army wind proof smock which makes a great stalking jacket. Being poly cotton is is, of course, not waterproof but it is also very breathable making it very comfortable and you are generally drier in it than in one of the gore tex shells. In my view gore tex has probably had its day for general wear.
Despite not being waterproof you can treat the fabric of the smock to make it water resistant and at that point it is waterproof for most stalking purposes.
today I gave diver Dave's spray on waterproofing its first test and so thought to post my initial thoughts. I'm in the Hebrides and went fishing in horizontal heavy rain. I had to give up after about an hour as I could no longer hold the rod side on to the wind and standing was becoming difficult, and a little dangerous in some spots on the loch side. I'm pleased to report that Dave's spray on waterproofing held up well in the most extreme of conditions. I had a fleece hat on and the hood of the smock didn't let any water get at the hat at all. On returning I'd dumped the smock on the floor of the car and the water was literally lying in puddles on it when I went to get out of the car. In a few places, at the back of the neck for example, the inside of the smock had started to become a little damp but the contents of the pockets were dry despite puddles lying on top of the pocket covers.
now it is impossible to make a direct comparison to the other options based on one day out but I would be confident that Dave's repel treatment will keep smock wearing stalkers dry for 99% of normal stalking use so it is well worth giving it a try.
Maybe once I get a few more wet days out I will post a more detailed review but in the mean time if you need to waterproof some clothing give diver Dave a pm and try his product, not only does it work well but you will be supporting someone who supports your sport.