There are a number of websites you can order tags from and they will ask for all the required details. Shearwell are who i and a lot of others use. The thing to ask is whether they are meat lambs, or whether they will be kept for more than 12 months of age (this includes for meat). Meat lambs under a year old only require a single slaughter tag with your flock number on, if staying til over a year, they need a pair of 'breeding tags' which have flock and individual numbers.