Hygena was a product of Humber Kitchens who changed their trading name
to Hygena in 1982. Later, MFI bought out Humber Kitchens.
I think Hygena units were latterly made by Howdens, an MFI spin-off,
who are apparently still in business. Perhaps this should be your
first port of call:
There is also a firm using the Hygena name, Hygena Kitchen Cabinets of
Allerdyce Road, Glasgow G15 6RX. Tel: 0141 944 8136. No web site.