Thanks Bloom,
I just rang a pharmacy and spoke to the pharmacist, it seems the brand we have is a prescription medicine and it's the only one there is. The dosage is much higher than the over the counter brands - to get the same dosage from the others I'd have to give him half the bottle!
My son gets a little bit of orange juice after the iron because vitamin C helps absorption, so I might try putting the iron in the juice. He sometimes refuses the juice but that might improve if he's not all worked up from having to take the iron.