The couple - who work a croft in the Highlands of Scotland producing daffodils and fresh produce, as well as being plant registrars for the RHS - showed a selection of their 500 historic daffodil varieties at the RHS Greener Gardening Show earlier this month.
Kate Donald said: "We have some varieties but don't know what they are. As well as seeing live collections for comparison - which will probably be in older gardens or estates - what would be really useful is any information. It could be just a list of names, the passed-down knowledge of a head gardener or an old bulb catalogue.
"Some of the varieties we have date back a long way. There was even one called 'Emperor', which was first published in HW's predecessor, the Gardeners' Chronicle."
She added: "If somebody thinks they might have an old variety, they could send us information or a flower for identification. If they have an unusual variety and are willing to part with a bulb we would be very grateful - we haven't struck gold for a while."
Contact: 16 Midtown of Inverasdale, Poolewe, Achnasheen, Wester Ross, IV22 2LW.