The forward movement side fins are still currently sold.
Fishmaster Style Paddle Pusher Fins for Tube Fishing
https://www.amazon.com/Fishmaster-Style-Paddle-Pushers-fishing/dp/B00EDQLMAO
I do not know how effective they are. I use a float tube quite often for fishing. I also use my standard scuba fins for propulsion. Slow trolling backwards in a float tube, is actually quite convenient and effective, because you are facing the fishing line that trails along in your path. Approaching waterfowl while facing backwards, not so much.