I did my ScubaPro technician training with Dive Supply, who are the ScubaPro distributors here, so that's where I go for service kits, etc.. However, you can't just walk in there since it's wholesale, so you'd need somebody in the industry to take you in. They're not in Kata, though--they're in Chalong (about 10 minutes away from Kata).
Yes, Dive Supply, the mysterious pretty (and big) warehouse out on Patak Road. It always catches my eye. For my first few trips to Phuket in 2008, I stayed in Patong, and I dove with “Sea World”. We drove past Dive Supply everyday on the way to Chalong. Then I discovered Kata Beach & Karon. I hope to be a Tech one day, and Scubapro is my flavor of choice. I would love to ask you a ton of questions about living and working in Phuket.