Recently completed B737 Classic to B737NG course with Storm Aviation, details on there web site, (
http://www.stormaviation.co.uk/training.html)
Also try the CAA site for 147 approved organisations.
http://www.caa.co.uk/
"search" type 147, there you will find a pdf files with the Part-147 Approved Basic and Type Training Organisations, this includes the contact details of the said training organisations.
And as to a later question, yes some do a B2 B737-3/4/500 to B737NG.