You might try a NAPA store, or someplace similar. That is, the local store that supplies the auto repair shops in your area. Stores like Checker and Autozone are good places to find car wash, and fuzzy dice, but for serious parts, you might have better luck at a NAPA. Of course, the staff will give you a blank stare when you say the words "Alfa Romeo". It would be helpful to bring one of the old, unbroken lug studs.
Note that the length of the stud will depend on whether you are running steel or aluminum wheels (wheels like Cromadoras or Campanoglas take much longer studs).
Might be a good time to replace your front rotors. I think most of them have the studs already installed and probably not that much more than what 4 new studs would have cost. I'm guessing that the 71s still had left hand threads on the left side of the car, which is probably why you broke them. As a teenager, I broke 2 or 3 of the LH studs on my '48 Willys panel truck before I discovered there was such a thing as LH threads. No reason not to switch to RH that I can think of.
As the car is a daily driver often ferrying grumpy wet and muddy kids I need belts to be safe but work properly as well.
I currently have the usual Securon ones and I found them very difficult, they twist often in the passing ring, they won't retract and lock too easily.
I decided to start...
I had the engine lid of my 1750 cleaned up and better painted this week. Under the paint they found this old (probably) paper sticker left there by the original seller in January 1969. Alec Mildren of Pymble Sydney. Sensibly my paint guy left it there.
I ended up buying these as I couldn't anything else suitable, they are quite expensive at £70 and the finish is so so. They will eventually be covered so am not too bothered. They fit fine and even with my 916 seats there is enough space on both sides. Found them on FleaBay, searching "door...