Chemo - How can I get a wig?

I am female, receiving chemotherapy & my hair is falling out by the handful. I have an HC2 form from the NHS so I should be able to claim a payment towards a wig. Unfortunately the wig supplies I have contacted all seem to be tired to one or a few hospitals & not the one I am attending. The one I am attending only has a choice of 2 or 3 wigs which are unsuitable. The wig supplies I found on line have much larger selections but cannot supply me as they do not cover the hospital I attend. Can anybody please give me some advice. Thank you