Here's a list of forthcoming rare plant fairs in UK (though sadly not one in Scotland):
6-7 Apr, 10am-5pm, Spring Plant Fair, RHS Bridgewater, Manchester.
7 Apr, 10am-4pm, Rare Plant Fair, Everingham, Yorks.
20-21 Apr, 10am-4pm, Spring Plant Fair, RHS Hyde Hall, Essex.
21 Apr, 10am-5pm, Spring Plant Fair, Arundel, W. Sussex.
25-28 Apr, 10am-4pm, Spring Flower Show, Harrogate, Yorks.
27 Apr, 9.30am-2pm, Plant Fair, Highgate, London.
More details at
https://www.plantheritage.org.uk/events/
