What constitutes "real" cider is a subject of debate, even amongst the real cidermaking community (!)
Basically though, it's cider made from 100% juice (as opposed to concentrate - as used in the popular ciders of today). Some real cider is still live (as with Real Ale), whereas most has been pasteurised, and some is made only from recognised cidermaking fruit (generally different from eating apples in that they are chosen for their bittersweet/sharp/tannic qualities (which help with making a balanced drink) rather than the qualities that make a good eater. Which is not to say that cider fruit aren't nice to eat. They're just not as nice to eat, in most people's eyes, as recognised eating varieties)).
Cider made in Herefordshire, Gloucestershire, Worcestershire, Somerset, Devon, etc, is generally made from "real" cider fruit. Cider made in Kent, East Anglia, etc is generally made from mainly eating or cooking apples (which isn't to say it's not as good, but it will taste different and whilst good, it's not my favourite - whilst being infintely better than most of what you find on the supermarket shelf).
Places to get cider from:
http://www.middlefarm.com/07_cider_perry.htm is a huge collection of cider and perry, near Lewes, which makes a nice day out. Cider from all over the UK is available on draught and in bottles. Get someone else to drive if you can.
Biddenden in Kent is probably our nearest producer, and pleasant on a sunny day www.biddendenvineyards.com/
The New Forest cider stall at Borough Market www.newforestcider.co.uk/ is good.
For mixed cases of cider, you can call my friend Paddy at www.hoppocketwine.co.uk/ he has a good range of cider and perry from Hfds Gloucs and Worcs, and who tells me that he will send cases for £5 per order. (I'm not on commission, but he is a friend of mine so I'm heavily biased here) I've tried his delivery service for presents, but not for myself (although I'm just about to order some English wine from him and get it delivered to work)
I hope that helps. If you've got any specific Q's, I'll do my best to answer them.
That's interesting. £5 a bottle is the going rate, I suppose, but it brings tears to your eyes when you think that it sells in Spain for around â‚¬3 a bottle (I'm trying to put the symbol for Euros here - three euros)