Not really close to Cranbourne but when I lived in Melbourne I used the Vet in Endeavour Hills next to the shopping centre. Don't go to the extended hours vet in Dandenong on Stud Road (between Heatherton Road and the Freeway). And if needed I had good dealings with the Vets in Narre Warren on the Highway near Webb St, they also run a vet surgery in Berwick, I have dealt with both of them and they were great.
Also in Hallam there is the South Eastern Animal Emergency Centre on Wedgewood Road, Hallam for after hours emergencies.