A search on the web for "roller bearing turbos" will show up suppliers in different countries.
I use a firm in NW London called Turbo Developments Ltd. TH eguy there is very knowledgeable and helpful- it was he who first told me about the overboost problem with other marques.
Price wise, in UK currency you can expect to pay around £600 for a regular 360 deg hyrbid and about £1,000 for a roller bearing unit, both on an exchange basis.