I bought the MC rebuild kit from Brooks Barn - they have been alright in the past with with seals and other stuff and i got my starter motor rebuild kit from them and not had any issues.
I looked at the price of a new MC - which was about £150. by the time you pay that it is almost worth considering a Brembo unit. So i thought i would take my chance on a decent second hand one which i managed to pick up at a reasonable price but it only arrived yesterday so i have not fitted it yet.
If you are ordering quite a few parts -
https://www.motorcyclespareparts.eu/en - are quite reasonable and have come out cheaper than robinsons (but i didn't know about the discount code before).
If you are after K Tech springs or emulators. Reasonable prices from
http://firefoxracing.co.uk/ and I have just bought some this morning from them. Was about £160 for both which i thought was good.