If you know a local farmer you could speak to him/her beforehand and agree that you take a couple of triplets, as long as s/he makes sure they had a good amount of colostrum. (and you would put them onto the bottle from day three or four and then take them away from the dam, and could possible supply him with some goatsmilk to supplement the triplets by tube while they are on mum - I have done it that way, and it worked well.)
With any "orphan" or spare triplet lamb you will take a risk that they didn't get enough colostrum.
You could also take a couple of ewes with lamb(s) at foot, and as said before worm them and only let them outside once their "10 or so days after worming" worm count is zero, and if your field is clean that should reduce the risk.