That is the latch that was on the Brisa/California Convertible convertible top. That top is on my 85GT. The company is long gone and it was never announced who got the parts when they closed. There are some aftermarket convertible top kit manufacturers that still make convertible top kits for other cars like the Miata. You might try seeking them out. If all else fails that part can be duplicated by a machine shop.
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "