Just wanted to add a cheaper/lighter option to the stainless steel locks, these billet aluminum locks:
http://blenddoor.com/product/miata_latch/
Full disclosure, I have not used them so I can't say with 100% they work BUT they look identical to the oem ones with one exception and that is the threaded hole on the edge that contacts the latch. It appears to include a allen head stud you can adjust to compensate for wear on the latch side. After watching the video on the above link I'm confident they will work.
I plan on doing this again(probably a different finish) and will try these this time around. If anyone tries the aluminum ones above please follow up with some feedback.
Also as a update on the unfinished latches, the new owner recently said they finally started to get surface rust but this is after two years and being in Florida probably one of the worst places for unfinished metal.