Good source is UK Hooks.
They sell the heavy Mono in 10 metre coils
I have found that mono seems to work quite well for tope traces if used with Circle hooks [Also available from UK Hooks] not the end of the world if the odd ones bites you off.
For the bigger ones we still use short single strand wire biting ends and J hooks. Wire bought in the states is quite stiff. The stuff sourced through military much softer,
Thought that I had run out a while ago, then when we moved in December found a couple of spools when packing up my loft, let me know if you want a few metres Alan/Rob.