Guessing you are talking about something at the tip to keep the boat from turtling ?
If so, a couple of methods I've used:
1. Quick and dirty - Tie a 1 gallon clorox bottle or milk jug to the webbing at the top of the sail (Make sure the bottle is sealed of course)
2. Sew closed cell foam into the head of the sail - I found about 1 square foot by 2" thick worked fine.
I don't understand why you'd want a mast float, it doesn't really matter if a Laser turtles, and it's pretty simple to prevent it. Infact, when I capsize to windward i find that that turtling the boat and bringing it up again is a much easier way of making the boom return to the water than waiting for the boat to turn into the wind.
Beginning sailors have trouble keeping the boat from turtling. Their reactions just aren't fast enough. Then once it's turtled, they waste a lot of time trying to get the boat back up. Frustrating if you are trying to teach a class of them. Along that same line of thought, shallow water is once place you don't want it to turtle - you can break your mast or mast step. I've seen it happen to more then one Laser, usually with newbies