@Flavius,
Personally, I find grip strength for kettlebell lifting pretty specific to kettlebells. I haven't found any supplementary grip work to have as much direct carry over to kettlebell lifting as actually lifting kettlebells. I think the unusual combination of support and cruch grip, the fairly thick handle, and how dynamic the grip demand is make carry over from other exercise less than might be expected.
Sure, someone who already has general world classs grip strength, like a John Brookfield, will be able to apply that strength to a kettlebell. But for a regular guy trying to really own the 24, or transition from 24 to 32, I don't think specialized grip exercises are necessarily the best way to go.
Don't underestimate the importance of the dynamics in swinging or snatching a kettlebell. It is the IMPULSE you have to deal with, not a static force, and it's hard for other exercises to recreate or help you respond to that impulse. This also means there is a large SKILL element with the kettlebell. You not only have to apply ENOUGH force, you also have to apply it FAST enough and at exactly the right TIME. Depending on specific circumstances, an ounce of improved grip skill can be worth a pound of grip strength. And you only develop that skill by doing lots and lots of reps.
Your dominant hand may be stronger than your non-dominant hand, but it is probably also more coordinated, skillful, and "learns" faster.
So I'd recommend just being patient and letting your non-dominant hand be your limiting factor. For most people, it will always be a little behind the dominant hand, but it will get stronger and stronger over time. If you want to speed the process along a little, you can do more sets on the non-dominant side (you can decrease the reps per set if necessary, but the idea to get a higher total volume on the non-dominant side). You can also do a few supplementary sets with the 32 if you are able to. These can be for low reps -- think of it as "teaching" that hand, not "working it out." Learning to snatch (or practicing the snatch) can also be a big help.
I think you will get more out of actual swings and snatches (and PATIENCE) than any other more static supplementary work. It may feel like your grip is "holding you back," but working within your limitations will naturally push back those limitations over time. It's an expected part of the process, not a problem that needs to be solved.
"Time and I against any other two."
-- Baltasar Gracian