I think the consensus is correct so far. You’re angry that you don’t have your car back (understandable) but nothing you’ve said indicates the shop you have it at is at fault. If you take a car in for repair, and the mechanic tries to get parts to repair it but cannot because the parts are not available, that is not the mechanic’s fault. You are punishing the wrong party, unless there’s something you’ve forgotten to tell us.
You certainly don’t have the right to take the car until your mechanic has been compensated for the work he’s already done. You don’t get that work for free just because you’re now mad at the situation.
If you show up with the cops tomorrow… Well first, the cops won’t show up for you because it’s a civil matter, and generally the police don’t show up to help you recover your property until you have a court order mandating that your property be returned to you, which you will not get unless you have paid the mechanic what you owe him and THEN he refuses to turn the car over.
As an aside, I also side with the others who pointed out that you made several bad choices here, including getting a low-volume oddball luxury car that you couldn’t really afford. If you want to play in the big leagues, you need money, and you didn’t have enough of it. I’m not reiterating that to rub salt in your wounds, but to point out that your anger and frustration seems to stem from the financial trouble you’re in. That’s not the mechanic’s fault, and he’s not likely to work with you to make this financially doable for you in some way if you infuriate him by taking pot shots at him.