||Yes we do.
We sell yellow rattle seed by the gram and it is available here: http://www.wildflowers.uk/yellow-rattle-c2x17864893
Best to sow onto prepared grass in Autumn at a rate of 1g per square metre.
Prepare the grass by cutting as short as possible and scarifying to expose the roots. Then sow and trample the seed underfoot. The rattle will then germinate onto the grass and flower in February.