Have they had their inital two doses 4 weeks apart, so you only need to booster them?
The smallest bottle you can buy is a 50ml one (25 doses). I keep mine in the fridge, re-seal with tape immediately after taking out the doses, and I use one sterile needle that goes into the bottle, 2ml is drawn up, I then take away the syringe but leave the needle inside the bottle (diffiuclt to describe in words), put on fresh sterile needle and inject. Then draw up next dose with syringe minus needle, using the needle still in the bottle. then again inject with fresh needle (I boil my syringes and needles for about 10 minutes just before use, transport them in tissue paper to keep clean)
Hope this makes sense?
At this time of year your agri merchant would have to order the vaccine in, as it is not the usual treatment time for lambs. If s/he is difficult about it being for goats go through your vets, they can prescribe it under the cascade system.
As far as I know you cannot keep Heptavac in the fridge, but then I usually need almost a full bottle of it so only use it on the sheep and buy fresh every time.