I would be horrified to hear of any vet dispensing antibiotics to anyone who had just walked in. I'm pretty sure it would be illegal, and for good reason.
It's one of the reasons we tell newbie livestock-keepers to get to know their vet as one of the first things they do, not to wait until there is a sick animal needing antibiotics...
So I'm sorry that you have had some stress not being able to get the treatment you wanted for your sheep, georgielmgm, but as others have said, you will need to either take your sick sheep to the vet or pay the callout fee.
Our vet charges £20 callout, but sometimes you can get it a little cheaper if they can drop in when they are passing anyway.
I often feel grateful that, with larger stock numbers, we don't have to worry too much if we need the vet for one; if you have only 5 sheep and need the vet, that's a big bill to spread over a tiny flock. But it's not optional, it's just something that has to be budgeted for.