Davey, currently the only source for tapered roller bearing replacements that are known to fit is through Winner's Circle
http://www.spridget.com/catalog/23.gif but there are other solutions in the works right now. Several people are working trying to find an over the counter replacement bearing that will work without any mods other than the thinning of the castle nut. I'll send you the information on what I had to do to convert my car. A bit of trouble but well worth it in my opinion.
'73 Midget (V6)
'59 MGA (I6) under construction
'73 Lotus Europa
"There is a fine line between a hobby and mental illness"