Talk to lancing marine. They have a website with contact details. They've sorted me out on numerous occasions in the past with my ford Lehman engine and I know they overhaul velvet drives routinely so suspect they have spares on hand.
Most bearings are "standard" sizes. Take accurate measurements of the ID, OD and width and have a look at www.bearingboys.co.uk
Failing that, pop into a bearing stockist ... there is one on most sizeable industrial estates.