The size of the threads of the cable adjuster (where it threads into the perches that are clamped onto the handlebars) is 7 mm × 1 mm. Moe Moore of Cycle Garden sells very nice stainless steel replicas. He also sells oversized 8 mm × 1 mm replicas for worn perch threads.
Cable adjuster for Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models.
Couldn't find the cable adjusterers on Cycle Garden's website, but a little searching found these from Euro MotoElectris. M7x1.0 stainless. May need a little filing in the cable slot (mostly the brake cable) but they'll work out.
Cable adjuster for Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models.