Yards for Calves to be Ringed
Rocer, even if you did get a vet they wouldn't be happy castrating animals who aren't properly confined. Is there any way you can improve your race by making a makeshift crush with gates? Or borrowing/leasing a portable crush/headbale? The problem is with m.bovis, BVD etc, people don't hire out yards as happily as they did in the past. Maybe ask your vet for advice - they will know all the tricks.
Castrating cattle beasts and sheep
(1) A person must not castrate a cattle beast or a sheep that is over 6 months of age unless throughout the procedure the animal is under the influence of pain relief that is authorised by a veterinarian for the purpose of the procedure.
(2) A person must not castrate a cattle beast or a sheep (of any age) using a high tension band unless throughout the procedure the animal is under the influence of pain relief that is authorised by a veterinarian for the purpose of the procedure.
(3) A person who castrates a cattle beast or a sheep must—
(a)be experienced with, or have received training in, the correct use of the method being used; and
(b)be able to recognise early signs of significant distress, injury, or ill-health so that the person can take prompt remedial action or seek advice.
(4) The owner of, and every person in charge of, a cattle beast or a sheep that is to be castrated must ensure that the health and welfare needs of the animal are met during the procedure and recovery, by ensuring that at all times a person is available who—
(a) has suitable equipment; and
(b) has the relevant knowledge, has received relevant training, or is under appropriate supervision.
(5) A person who fails to comply with subclause (1) or (2) commits an offence and is liable on conviction,—
(a)in the case of an individual, to a fine not exceeding $3,000; or
(b)in the case of a body corporate, to a fine not exceeding $15,000.
As others have said, it's difficult to get calves that size ringed because the testicles have grown too large. If you only manage to get one trapped in the ring you end up with a rig, you definitely don't want that. I believe the animal welfare regulations say they should be ringed at less than one week of age also.
Edit to add - at this stage I think it's a vet job, they can sedate them if the yards aren't up to scratch.
Did you know, that what you thought I said, was not what I meant :S
I had a cryptorchid calf done by a vet a few years ago, knocked him down with some sedative, did the job lying on the ground. Otherwise they've all been done standing in the race. Just be careful not to get a kick to the head if you give one of them a fright.