Hi Paige - I am based in the North West area, just a question - did you mean clasess in terms of lessons? or classes in terms of competing?
If lessons: the S&CBC as noted above are a good place to start, you'll find some likeminded ladies there, and am sure that the grounds that they are based on can accommodate you with gun fit/lessons/coaching etc... There was a recent Shotgun and Chelsea bun club day booked for Manchester Clay Shooting Club which was cancelled - it will be re-arranged - a new date should be announced soon. I am planning on attending - the idea of cake, tea, fun and shooting has drawn me in! Many shooting grounds offer lessons, these can either be group or private, there should be some information following the link that Jon supplied above.
If competing: The registered sporting shoots that I go to unfortunately don't have a ladies competition class - generally as there aren't that many of us competing. However, as they are registered shoots you compete with shooters that are in the same classification as you. You do find that most charity shoots, gamefairs and the major competiions (like the British open, Classic etc..) have a ladies category.
Hope that doesn't confuse things!
Where abouts are you based?
Sam