I think you can take the advice given by Toto CS as gospel. Here's what I'd do if this was my potty. First, I'd rig a cord from the flapper chain to the top of the tank so I could flush manually while getting the need repair part. This is not a classy or permanent fix, just something to get by. Next, I would either find a new handle locally or order one from Toto. I really don't know if a generic handle would fit or not, but it would be easy to find out. Just take the broken one with you and go shopping in plumbing shops.