Hello Adam,
Sorry to hear of your plight.
A couple of points as I see it:-
‘…tyres almost worn to the limit…..’. It used to be that car retailers had to ensure any (non-trade) vehicles retailed had to have a minimum of 3 mm of tread remaining at the point of sale. Still is?
If it had been mine, once the locking wheel bolt became over difficult to remove, then I would have returned the vehicle to the retailer under the 90 day warranty, and requested that they remove the locking wheel bolts.
If they ( the retail dealer?) have pointed you to a specialist, then why not entrust the car back to the dealer, and request they arrange with the specialist.
I’m not sure why you should feel wary of the recommended specialist -?
Mc.Gard? Well proven supplier. Why not look up their contact details and give them a ring? Alternative:- it wouldn’t surprise me that the specialist would be well versed in the availability of replacements.
Perhaps you could let us know how you get on Adam.
Kind regards,
Gareth.