You get Sierra Madre Coupons at the Dropbox (1000, each hour or something) in the abandoned bos Bunker. There is also a vending Machine in the abandoned bos Bunker. You can get Infinite weapons repair kits there. Also great for making Money.
Thanks for the tip. I have played Fallout NV for almost 500 hours and never found the abandoned bos bunker. I'll definitely have to check it out. Thanks for your comment