hi andy - not an experienced shpherd here but - all advice given to me is out, out, out! especially if you can provide windbreaks and shelters.
....as for the Macs, you say you will have to order them...in the interim why not use placky bags (tescos etc)
Just cut one of the bottom corners off for a head hole, then make slits for the front legs near to the oposiste corner, and the handles for the bags work as read legstraps to keep the homemade mac in place. Gok Wan may have something to say,,, but function wins every time in my book!
at least you can get the little darling out. also if you can use the same branded bags for siblings, but vary among the flock then you can see instantly that the lambs are with the correct mum!
HTH Emma T