Bristol Temple Meads and Cardiff Central are now the only stations that I know of with no bins.
I'm not sure if I remember correctly, but I think I have seen large wheely bins on the platform at Cardiff Central once or twice. It can be quite hard to find a bin on the railway though.
The suituation on trains is little better than on stations. There are bins but they are hard to find and few in number (normally between seat backs, but not at every back to back seat, as far as I remember, or is that just Arriva Trains Wales 158s?).