VeloTech of Paso Robles, California in the USA has the solution for roughly USD 10,000 and can transform your current 911 Convertible to be a true targa. The new carbon fiber roof can be partly removed to reveal the roll-cage / B pillar and wrap-around rear window. VeloTech, a Euro brand turbo-charger firm, announced at last year's SEMA show that if they can drop the price to USD 6,000 the demand will follow.
The targa came about after US government set some strict safety regulations in the 1960's about top-down driving which made it impossible car manufacturers to continue making traditional cloth-top convertibles. In due time manufacturers raised the safety of their soft-top convertibles to meet the new safety regulations resulting in the return of the cabrio.