Kerosene level indicator ball (Llynclys SY10)

I have an Atkinson oil level indicator on my Kerosene tank, but have lost the little green ball that floats on top of the oil in the transparent pipe. Does any one have a spare, or know where I can buy one in Oswestry? The ball is about 6mm diameter, made of plastic, and is vivid green in colour. Thanks, iain, in Llynclys 07940 722160