This isn't an 'off-the-shelf' solution, its more of a DIY thing.
I do have faced a time when I didn't want to get rid of my shoes because they were intact, it was just the sole that had worn out and would slip often than not.
First ensure that they aren't structurally damaged. Is it really going to help longer term if you somehow manage to improve grip?
If they are good (as they always are), and of course if you are okay with getting rid of its existing grip, you can try what I have tried years ago.
- Clean the sole. Remove/Scrub off anything from it. Including the (broken) hard rubber that came with shoe when you bought it. Make it plain. After this the sole should like what you have on a shoe that you use for playing tennis, a flat sole.
- Use the best shoe goo you can find, seal any leaks if there are. Apply shoe goo allover the sole and attach a thin rubber insole over it. Let it dry.
- Get similar type of antivibration rubber pads, they are pretty cheap. Cut them and stick them at the heel and on the out sides of the shoe. (On Left sole left corner. On right sole, right corner). These rubbers work so well to improve the grip on the sides of the shoe.
- Find another set of rubber pad that people usually use for furniture. The size and shapes for those may vary from what I can find here. But, look for something which is not extremely hard. Cut it in a shape of the heel of the shoe and stick it using shoe goo.
- For toe part again use the same antivibration rubber pads, but in a horizontal manner. That improve the grip on toe side, makes life easy on sharp descends.
- One all layers are glued perfectly, use a sandpaper to level them up.
This worked for me. But I only preferred to use those shoes for dry conditions, didn't want to risk a thing.
The durability will depend on factors like Usage, way of storing when not in use, quality and harness of the rubber, quality of the shoe goo (adhesive) and of course craftsmanship.