If you like your Simms with felts try searching Amazon for crampons, they have an excellent selection of slip on grips with all types of cleats from aluminum to carbide and they are pretty reasonable. I tried to link to the page but.... technical difficulties.
I wonder Gord, or anyone else for that matter, have you tried such crampons on your wading boots? I've seen purpose made for wading boots that look something like galoshes, I did own a pair, may have them still, they worked ok. These had tread like aluminum bars and cost about as much as new boots. The crampons for hiking boots look like a great value though I wonder how long they will stand up to rocks etc - at least the ones that use bungee cord.
I do still have them. Photos:

