This is long after the orriginal enquiry but I am interested in silkworms and have been researching them for over two years. I rear some each year and take them to craft fairs, giving talks about their life cycle rearing and how silk is produced, as I am a silkweaver.
They are/can be difficult to obtain, but two or three companies do supply. the most reliable being 'Oxford silkworms' a company which is part of 'The Jungle' in Abbingdon, Oxon. www.junglereptiles.co.uk. At time of posting they are having trouble with customs and Exise, but intend to keep supplying when 'things' are sorted. They also supply artificial food in powder form which is a good substitute for mulberry leaves, which are indeed difficult to find in the UK. Worldwide butterlies - on the internet - WWB.co.uk will supply mulberry plants to grow.
Hope this is of use to someone.
Regards Maggie