In reply to Kahti:
You can book all the courses on their own - less than one minute on the BASI website reveals that there are 9 Snowboard Level 1 courses running between now and the end of the year - some of them UK snowdome based so you could actually get a head start on everything before the winter.
Back in the day gap courses didn't exist and that is what everyone used to do - sadly that culture of doing a course or two (enough to get a job somewhere/anywhere) and then actually working as an instructor and gradually working your way up the quals seems to have been replaced by a culture of 'do a course then go on enough training courses to go and do your next course and do the bare minimum hours then finish up with a high level qual without really having any experience'...
Personally I would highly recommend the DIY approach if you have a good background of riding/sliding. Way cheaper (by a long way) and generally much more fulfilling and interesting.