One checks around, gyms and other fitness oriented places are good places to look, and one gets one for many different reasons (choose one or all): weight management, diet management, nutrient analysis and recommendations, other diet related issues.

I've been seeing her a little less than a month, mainly to tweak my vegan diet, ensure I'm getting the right nutrients, and look into some of my intestinal issues. Don't know enough about your health care system to know if they'd give you one, but you could always check with your primary care physician to see if s/he'd recommend a nutritionist to you. And getting the analysis done would likely help with a diet related issue. I'd also recommend Becoming Vegan by Messanto and Velina (?) as that will cover diet related issues and would probably be cheaper than a nutritionist.