My 93' K1500 Silverado Extended Cab has a drivers side fuel tank, but I would like to add an extra tank on the opposite side for extra fuel capacity. Would this be possible? If so where could I get one?

Almost anything is possible with enough money and ingenuity, but in this case it wouldn't be practical. If you crawl under your K1500 I think you will find that the exhaust system pretty much occupies the passenger side space where the gas tank is on the driver'* side. After GM was hit with a class action lawsuit over outside the frame rail saddle tanks on the squarebodies, they did away with dual tanks on the gassers. I had an 84 K20 HD camper special with the dual tanks and I loved the setup, never once worried about the risk of fire. Hauling a 3000 lb. in bed camper I got around 10 mpg and with a camper on it was a pain at the pump to try and fill both tanks, so I ordered up some neoprene hose, picked up some copper T'* at the hardware store and tied the 2 tanks together, both the fill and vent hoses. I was able to fill both tanks from one side so it didn't matter what side of the pump I pulled up on. Made it a lot easier when hauling the camper when your range on one tank was <200 miles.

I've heard of folks on the diesel pages putting in an additional tank above the spare tire and in place of the spare tire. I wouldn't personally exchange the spare tire for a reduction in fuel stops, however, it is an option. Some of them mount the spare elsewhere, like in front of the grille or on the roof. Those guys usually have long-beds.

With enough ingenuity, you could get the exhaust system outside of the frame rail, perhaps with a series of narrow mufflers to do a similar job as the one big one . . . ? Doing this would really be wild though, and would likely lower ground clearance by a few inches where the exhaust crosses under the frame.

Can you take up some of the bed with one of those in-bed tanks? Depending on what you buy and what size bed you have, you can put like a hundred gallons there.