Hello Budrew. Your question inspired me to do a little research. Yes, hardware stores and arts & crafts stores supposedly carry silica gel, though I have never noticed it anywhere. A guy on ebay is recycling the stuff for about 10 to 25 cents per packet if you purchase in quantity.
Silica gel is waaaay cooler and waaaay more important than I ever thought! I'm now contemplating starting a distributorship to help fellow A'goners protect their valuable stored gear. But, I'm too busy with other things for now.
Silica gel was invented just prior to WWI for use in gas masks for the Allied troops. Again, we used it during WWII to keep penicillin fresh for our troops. Since WWII, government and industry have found a wide number of uses for it, such as: keeping a lot of medicines fresh, "mothballing" U.S. Navy equipment; preventing expensive optics from fogging in cameras and rifle scopes; preventing mold and mildew in fine leather and clothing; protecting the contents of vaults; maintaining artifacts in museums worldwide; protecting expensive food items from mold and worse; and most importantly (to me) protecting electronics from rust, corrosion, pitting, staining, and oxidation.
Silica gel comes in two types: indicating and nonindicating. I prefer the indicating type because it turns from bright blue to pink as it becomes full of water vapor, signaling it is time to recycle.
Silica gel lasts forever. You can recycle it in your oven to remove the water vapor, and the indicating type returns to its original bright blue color ready to do its job again.
People just don't realize that high humidity results in microscopic water droplets all over their expensive equipment. In a sealed bag, box, or closet silica gel can be very effective in maintaining a desirable relative humidity of 40-60%, and the indicating silica gel makes it easy. You need 40 grams of silica gel for every 3 cubic feet of sealed environment that you want to protect.
If I ever get busy marketing my wooden audio shipping crates to A'goners, I will definitely include silica gel as standard equipment. Who would want their expensive electronics sitting on some damp dock when it is raining outside? Not me.
No wonder these little packets come in so much stuff :)