At the advice of the Dr at the ataxia centre I have started taking 2g of Nicotinamide a day for energy and I have to say I have really noticed a difference. To reorder online I ordered 500mg tablets (the largest I've found - I have to take 4) from a company called Health 4 All, 180 tablets (so 45 days worth) was just under £10 (and I have a code for 10% off next time too - DISC2014) but what impressed me is that it is in a flat plastic 'jar' which easily fitted though my letterbox meaning I didn't have to traipse to the sorting office to collect it.
Would definitely recommend.