He should have recorded all the ear tag numbers of all the sheep on the movement license. You'll have to get him to give you tags for them; I'd get him to come and put them in for you, or at least lend you his ear taggers so that you can do it. And if you haven't done it before, it would be best to get him to show you how to do it.
All the different makes of tags need different taggers, so unless you are certain that you want to use the same type as he does, don't let him get away with just supplying the tags, make him lend you his taggers so that you can put the tags in their ears.
If all the lambs are for selling or eating, they'll need a single electronic (yellow) tag each. If you might want to keep any of them on, they'll need two tags, one in each ear, of which one must be the electronic one and the other is non-electronic, with the same number on it.