Loads of venues around our way run them...They won't necessarily be advertised as 'Intro' classes though, as that term relates to the schedule category more than the classes themselves
Have you seen any of the Amateur Qualifiers around ? They are quite often run in conjunction with Intro schedules...although not always
Take a look at this website www.hargateequestrian.co.uk they have a show this weekend and on the sunday they have a 75cms and 85cm unaffil classes and then a 90cm Amatueur Class......