Hi
If you can't find one on recomendation pick up the phone and start calling round a few. If the person on the other end of the phone doesn't sound like someone you'll get along with then hang up and call the next. It's a gut instinct thing. If they're not willing to chat to you and explain how they run things then it's not the agency for you. Ask them questions, give them senarios, and of course, laugh heartily at them if they tell you there's a joining fee! Any agency who looks after they're staff well will be happy put you at ease.