I'm not sure if clovertox is available any moere, it might be one of those taken off the market.
Another alternative that is claimed to do the job is "Westland lawn weed killer" It's apparently a spot weed killer rather than a general spray, so it may not be suitable if you have a heavy infestation.
A tip a groundsman gave me once is to "bleed" the clover first by criss-crossing it with a pen knife.
Hope thats of some help Tbird+