Ben Krasnow on Twitter: "You can still buy low pressure sodium lamps (eg on Amazon), but the ballasts are expensive and rare. I found that using a cheap CFL ballast, and replacing
Amazon.com : Ultra Sun HPS 1000 Grow Lamp - Full Spectrum High Pressure Sodium Lamp, Ideal for Plant Growth, 1000 W : Video Projector Lamps : Patio, Lawn & Garden
iPower 1000 Watt Pressure Sodium HPS Grow Light Bulb Lamp and 1-Pair 8-Feet Rope Clip Hanger Combo Set for Indoor Gardeing Growing Light Fixtures - Downtown Hudson, NY