Justin, do you have anything heavier with which you can test your max? Knowing your max reps with a few different weights is helpful here.
If you don't have a 28 or a 32 but you do have some weight plates and duct tape, you can rig up something. I used standard (1" hole, not Olympic) plates to make myself a heavier kettlebell back in the day. Two 5-lb plates turns your 24 kg into a 28.5 kg bell.
(If you decide to do this and want instructions, reply here and I will try to post them - if you do it correctly, it's actually quite solid and useable. You can buy two 5-lb plates for $10 at a local fitness store if you don't have.)
One thing you could do, although it won't be as good as knowing how many reps you can currently get w/ 28 or 32 kg, is to test your max reps with 24 kg. It is, to quote an old book by Pavel, better than a slap in the face with a wet fish (or words to that effect).
Make sure you are properly rested then properly prepared for a max test, whichever one you do.
-S-