Im not sure whether you are still interestedin this or not but I'll answer it anyway.

You need to have students working on an NVQ in order to get the A1 andA2 assessor awards as part of your training. So if you have NVQ's in your shop then you have the hardest part cracked.
You cannot mark NVQ's work if you are not an assessor, however you can write them lots of Witness statements that count as evidence towards their qualification.
To be able to teach/assess you need to be qualified to the level above that which you wish to teach. So if you want to assess NVQ 2 you need to have level 3 at least. Most colleges though wish you to be qualified to at least ICSF before they let you loose on students.

Hope this helps