I am not sure about "chewable" forms of electrolytes, but if a tablet that you'd swallow is OK, I recently tried Endurolytes on a long, hard ride in 95-degree weather and they worked fabulously.

I've also tried Nuun dissolvable tablets. They seem to work really well for my husband, but I like Endurolytes better. Adding Nuun to my bottle just seems to make me have to pee a lot more than I normally do.