I'm not sure why this is so difficult. There are literally 5 other tire models available at Tire Rack in the sizing in which you're interested: Pirelli P Zero Rosso, Yokohama A008-P, Yokohama Advan AO52, Pirelli P Zero Trofeo R, & Pirelli Cinturato P7. Some are as racy as the Proxes R888R you don't like (though they're not listed as such), but not all of them are. Admittedly if you're looking for rain/snow/4 season tires, you may be somewhat out of luck.
https://www.tirerack.com/tires/TireSearchResults.jsp?tireIndex=0&autoMake=Porsche&autoYear=1987&autoModel=911+Turbo+Coupe&autoModClar=&frontWidth=205%2F&frontRatio=55&frontDiameter=16&frontSortCode=44950&rearWidth=245%2F&rearRatio=45&rearDiameter=16&rearSortCode=46400