The short answer would be "my house" as we are now in the process of liquidating almost everything we own before we head off to travel for a couple of years. Here's where I have noticed that most 'survival-minded' people shop for their gear/supplies:
- Garage sales. This is an excellent place to shop for nearly everything the survivalist could need including gardening stuff, tools, outdoor gear, household goods, etc. You never know what you will find so it takes a bit of patience to get the "good stuff" but the best things about garage sales is that you buy your stuff on a cash-only basis (no pesky security cameras or credit card paper trail to immortalize your purchase).
- CraigsList. Similar to garage sales, you are buying (usually) used items but people really do list the most wide-ranging list of items on this popular website. Again, these sales are anonymous, cash-only, no names sales that can net you a lot of great stuff without the Big Brother part.
- Private sales. Word of mouth can be a great way to sell/buy what you need. Just letting friends know you are looking for a _____ or you want to sell a _____ can bring buyers or sellers to you rather quickly. Buying and selling firearms this way is, as Martha Stewart would say, a good thing.
- Thrift stores. Another good option is your local thrift store where items may be new (but are usually used) and they are generally much cheaper than what you would find in a regular store. Use cash, not your credit or debit cards here as well.
- No-name stores. This category includes small businesses that sell antiques, re-sell items (generally that the owner has gleaned at estate sales and auctions), etc. Usually these stores prefer cash sales but they often accept credit cards as well.
- Auctions. My granddad couldn't pass up a good auction. There are plenty of deals to be had if you know what you are doing at an auction and while these places are more competitive than garage/estate sales, you can also walk away with some pretty good stuff for very little money (depending...I usually avoid auctions in cities as everyone and their brother comes to these and often bid up to more than the value of an item which is both annoying and flies in the face of getting a good deal).
- The big box stores. Sometimes you just need certain items that you either can't wait to buy at the places listed above or can't find. So off you go to the local Walmart or Home Depot to acquire said items. A caveat...shopping at these places will create a digital trail of your visit. If I had a quarter for every murderer who I have seen on surveillance video at one of these stores buying duct tape, zip ties, a shovel, a garbage can, sheet plastic...you get the idea.