If you take the Cambridge Combined Science IGCSE (which is available to private candidates) you can sit the following papers:
Paper 1
Paper 2 (allowing you to obtain grades C to G) OR the harder Paper 3 (allowing you to obtain grades A* to G)
Paper 6 (which replaces coursework or a practical examination)
You can download the syllabus from here:
http://www.cie.org.uk/programmes-and-qualifications/cambridge-igcse-science-combined-0653/
To find an examination centre, start here:
http://www.cie.org.uk/i-want-to/find-a-cambridge-school/
(You'll probably have to contact individual centres, which are likely to be independent schools, to ask if they'll accept external candidates and explaining which papers you want to sit).
IGCSEs have the same status as GCSEs, so they're equally acceptable for entry into teacher training.