Like the guys said the options are as follows:
1. Take out a second 'regular' policy. You can only use your total NCB on one policy at a time. Alternatively some insurers will allow you to share/spread your NCB over two policies. e.g. if you have 4 years NCB, they will allow you two assign 2 years NCB each to two policies (really just moving the goal posts)
2. High excess policy -no NCB required. That xs direct offering seems to be becoming more exclusionary with what it will cover, and increasingly moving away from the one price for all structure
3. Trade policy -as many cars as you like...start buying the fleet now!
If you were going to run an FTO and a TVR I'd think option 3 would be most suitable -your best bet is to speek to a broker and explain your requirements. They should be able to advise the bset fit.