Antibiotics won't help coccidiosis because coccidia is a protozoa and not a bacteria.
Wait and see isn't good advice. Eating a single oocyst will kill thousands of cells in the intestine. Eating a large number will kill millions of cells causing bleeding into the intestine which is when you see blood in the feces. They won't get sufficient nutrients from feed and become anemic making them susceptible to other infections.
You may want to read this to become acquainted with the protozoa which in in soil worldwide.
http://www.chickenvet.co.uk/health-and-common-diseases/coccidiosis/index.aspx
All feed bags that are medicated (with a coccidiostat) should have it printed right on the front of the bag and at the very least it should have the word 'medicated' printed prominently on the guaranteed analysis/ingredient tag.
Some feed stores only carry medicated feed, some only non-medicated, some both.
The oocysts will show up in the feces whether there is blood or not.
Any age chicken can get a case of coccidiosis if they are suddenly exposed to excessive amounts of coccidia of a species they haven't previously been exposed to. Light exposure allows them to become resistant.
Chicks raised by a healthy broody hen will get probiotics from consuming some of her feces.
Most vets, even avian vets have little experience with poultry.
That said, vets should have experience with coccidiosis since it affects all animals with contact with soil - dogs, sheep, goats, cattle - even humans.
No grit in starter because the ingredients are already well ground.
I always offer grit to chicks regardless of what they're eating because it helps to develop the gizzard.
I don't know if the product Corid is available there but they will have another product that contains amprolium (active ingredient in Corid).
They may just call it amprolium or there is this product.
http://www.iahp.com.au/australia/feed-additives/keystat-powder-keymix
I thought sand was pretty much everywhere. Bird grit will work for chicks up to about 5 weeks, then they need something larger.
Feed stores should carry larger grit.
As birds eat, the tongue pushes it into the esophagus and is temporarily stored in the crop. It then passes into the proventriculus (first stomach) where it gets digestive juices to help break it down. Then in goes into the gizzard (mechanical stomach) where strong muscles compress the tough inner membrane against the feedstuff to grind it. Grit of the appropriate size gets lodged in the gizzard to aid in grinding the food. If the grit is too small, it will pass right through the gizzard and won't help. Not having appropriate grit, some things will pass right through without complete digestion and they can lose benefit from some of the nutrients in the food.