You'll need to find a NV CFP instructor to qualify you with additional firearms. All of them charge a fee for it. I was recently added to the LVMPD approved instructor list. PM me for details if you're in Clark County.
You will have to find a Nevada CCW instructor and go through live fire qualification just like you did when you took the intiial CCW class. Instructors will usually charge for this. but sometimes not if you were a former student. Normal rate is $25-$35.
After you qualify, you must take your certificate to the Sheriff's office. I know Washoe County charges a flat $15 fee to add as many handguns as you want.