Anyone know a cheap source of 26" tubes for upto 1.5" tyres?

Hi I'm just looking for a couple of tubes for a city commuter machine of mine with 26" skinny slick tyres - many of the cheap 26" tubes these days are too fat (and too expensive for a cheap hack, and the Presta valve has failed on one of my existing tubes, making repair not feasible).

I have tried Poundland and Wilko, and will pop into my local Asda superstore next (all are my usual known local cheap sources of cycle accessories to get me through the winter on my commuter scoot without spending too much on it).

Thanks