A while back, I searched high and low to see if anyone had Merkel rods for sale, and struck out. Best bet might be to find another gray marble with Merkels and use it as a parts table, but finding one that is cheap and Merkel-filled is probably going to be equally difficult.
If it were me, I'd get a new Tornado rod, replace the bent one, and then keep my eye out for future Merkel opportunities.