I can't really advise about teacher training, as I haven't done this myself.
However, I can't stress enough the importance of getting some school experience, on a regular basis. I volunteered one day each week in the reception class of my DC's school, for a year and a half, during which time I retrained to be a TA.
It's invaluable, not only in familiarising yourself with school routines, current issues, and observing the practice of others, but also to establish whether it really is for you, and also what age group you'd like to work with.
I got a paid job earlier this year as a TA in KS2, and I've discovered that I do actually prefer this age group to Foundation Stage (although I feel disloyal saying that 
). If I hadn't done the voluntary work, I wouldn't have been able to compare the two and I could have enrolled on a 3-7 PGCE and then found I was teaching the wrong age group for me.
Lots of heads will be more prepared to talk to you if they vaguely know who you are. Do you have any way into a local school (e.g. do you know any teachers at a local school, PTA committee members, governors, know anyone through a church or community group?)? I'm sure there are people who just write to a local school and ask for voluntary work, but based on the experiences of people on my course, it tends to be easier to get a good voluntary placement if you have a 'way in'.
Good luck, I hope you get on well with it.