TC tumblers are very hard to come by. Have been told that Lyman tumblers will work, but need to be modified to fit the TC hammer.
Have seen a number of TC tumbler half cock notches and sears damaged from dry firing with the lock at half cock. Trigger strikes the sear, and all the stress is put on the notch and sear tip. Just a matter of time before it chips or breaks.
A couple of folks with broken lock parts told me they saw a YouTube video demonstrating how to place the gun in half cock dry firing the gun when adjusting the set trigger. TC recommend this method years ago, with S&W now taking the position the tumbler or sear ‘shouldn’t break’ doing limited dry firing, but if it does, too bad because there are no spare parts. Got to love YouTube.