Talk to the receptionist. Tell her you are concerned about mite infestation since this IS a petshop pig and the information you have gathered off the internet says skin scrapings are painful and often false negatives so you would like to treat them with ivermectin due to the situation and broken quarantine.
Then give her the weights of all 3 pigs and request 3 doses for each pig (10 days apart). Ask her to check with the vet and get back to you so you can run in and pick up the ivermectin and 1cc syringe. (My vet just jots down the amount to give next to the weight of each pig, that´s why I recommend giving the weights)
Try it. All he can do is say no, then you can have Lynx help with the horse paste mess.
It is all the same stuff. There is oral and pour on ivermectin that is just diluted a bit more -- uses the same ingredient to dilute that the injectable does.
Try the vet. I read about people trying to use the dose info I have, even read a vet saying, "yes follow those directions, they´re fine" and then I see that they have figured it out wrong. That´s why the vet should be your best bet.
I hope he will be willing to provide you with doses for your pigs. Nuts, do you get oral doses or do you have to give an injection?