I am surprised the breeder did not arrange for Hachi to be desexed before Hachi was sold to you.
I'm assuming they sold the dog to you on the understanding that it was to be a pet only and not for making more puppies? Ie they did the right thing again - and stopped using this dog for their breeding program and homed it (so they thought) into a non-breeding home? Their alternative choice was to get Hachi PTS so that no further puppies would be made from Hachi's genes.
And now you're jumping up and down all angry because the dog has problems which mean it should not be bred and might not live a healthy life?
The breeder has already done the right thing as far as providing you with a healthy puppy is concerned - they offered you a full refund and to take Hachi back - which you refused. You have to stop assuming that the breeder was deliberately up to no good - you will only make them unhappy with you and far less likely to co-operate.
It's hard to tell from what you wrote - which vet took the xrays and who paid for what.
If you paid for xrays and you (or the vet of your choice) did not receive those xrays - then you are entitled to a refund of the xray money. If the dog has had two sets of xrays and the ones you haven't got are the first set done by the breeder's vet and paid for by the breeder - I don't see anything wrong there, the breeder probably has (or had) them.
My doctor - gave my xrays to me to take home. There are some digital ones out there (of my nose when it got broken) but I don't know whether they were kept - seems unlikely as disk space was very expensive back then. I've got all my knee ones.
So chances are the Breeder's vet won't have the xrays because she would have given them back to Hachi's owner at the time or whomever paid for the xrays the first time around. It's frustrating but the requirements for record keeping with vets is not as strict as for doctors specialising in humans.
It is true that vets do not like to offend their best customers - so they will sometimes tell their customers only what they want to hear.
If your vet thinks there is a problem with the other vet's competence they can write to the Australian Veterinary Association.
It is possible for a small dog to do just fine without a hip joint. Or if it is kept lean - do fine with all the dodgy joints and the surrounding muscle will compensate. It's not like it is a Rottweiler which is a size that puts stress on the joints just by being big and heavy.
I think you are guessing at reasons for things that have happened that probably aren't true, and that is hampering your efforts to get things sorted out.