I just bought a pair of Mazda MX-5/Miata (NA) front uprights which I intend to use in my one-of project.

What ball joint could be used for the top wishbone? (preferably a stock car component with dust protection)

As the lower bal joint I`m intending to use a stock MX-5 component but the upper ball joint is integrated/pressed to the wishbone so I need other solution.

check out this threadlinky

We have used the BMW 7 series drag link ball joints as they are a perfect match.

Matt