A few days late on this but if you are not sorted....
if you only need enough for two, why not try your local (large animal) vets.
Ours will supply the amount we need (or want) . maybe at a slightly premium price but better than fly strike.
and the official shelf life after opening for Crovect is 3 months, (for CLik 1 yr) - for two sheep even a small bottle is a waste.
Also if you are late shearing and intend to do so, you should not use a pour on ... most preclude shearing for a number of weeks after application .. this is one of the first things our shearer checks for his own H&S.