Rubber or silicone strip 1-2cm wide, 20cm long, 0.5cm thick (Huyton L36)

A piece that I could cut down to size might work too. I need it to attach two lights to my bike handlebars. As the clamps don't fit properly, some rubber is needed to make gaskets to go around the handlebars (see photo for example of what I mean). I have tried using Velcro straps as a gasket, but because the handle bars get thinner towards the handles, it slips and works it way loose, and I hope rubber or silicone would stay in place better. Can pick up in Liverpool and St Helens areas. Thank you.