Amid Cuba’s months-long fuel and electricity crisis, one of the island’s most iconic exports is feeling the pinch: cigars. Retailers say the industry is facing one of the worst supply squeeze in history as blackouts, fuel shortages and shipping disruptions make it nearly impossible to produce luxury cigars and get them off the island in the temperature controlled conditions they require. “I’ve been telling clients, ‘Listen, it’s been months since I can get them,’” said Manu Harit, a London-based cigar specialist whose business is almost entirely built on Cuban cigars. Over the last year, he said, orders have been filled...