I had a '62 Re-issue Jap-Strat that sounded as thin as a twenty-year-old T-shirt until I replaced the tremolo with a solid slug of brass. I milled the piece myself. I've never seen such a thing in the stores.

There's a block of metal screwed to the underside of the bridge plate. To lock the trem, you need to stuff a piece of hardwood or brass between this block and the guitar body. To keep it in place during string changes, it helps to remove the tremolo springs, and have some dense foam stuffed into the gap on that side of the tremolo block.