1) To the best of my knowledge, there is no review service or website for drivers.

2) Re: driver + car rentals - Kangaroo Cabs is a good choice. The drivers are experienced, professional, and reliable (I can attest to this from personal experience, as well as that of many local and foreign friends). However, they are one of the most pricey options, costing about LKR ~12,000 to 13,000 per day or so (~USD 90).

3) Re: getting a driver alone - I can provide the contact details of a reliable "rent a driver" service, which I use myself when going on long-distance trips. Off the top of my head, the price is between LKR 2,000 to 2,500 per day; it is also customary to provide the driver with a small amount of additional money to buy lunch and dinner.

Note: I am not sure if providing such details is against the forum policy; if so, my apologies. Just to be clear, I am a doctor by training and the current CEO of a medical education tech company; I have no hidden interests.