For all you rookie sellers out there, let me tell you - I started selling on ebay only 18 months ago, and I never seem to find problems finding stuff to sell. Afterall, remember the golden rule - one person's trash is another person's treasure.
First, I have four children each one of whom are name brand freaks. As you probably know, we can't stunt their growth and they have this nasty habit of outgrowing, rather than outwearing, their clothing. Shoes are probably an exception here, but has been known to happen.
So, I tell my children - go get anything from your wardrobe that no longer fits you, you no longer like, or haven't worn in 12 months. The reward for parting with the clothing they will never wear again? I replace it from other sellers' stock on ebay. This way I am able to keep up with the insistance for name brand, and a fraction of the cost which is usually subsidised by the sale of the clothes the kids have outgrown.
I do the same thing to my wardrobe, especially lately - been on this magic diet that is making me go from a size 14/16 to a size 10/12. Not a bad thing overall, and my reward is replacing my large clothing with much smaller clothing.
Apart from this - I scan the house every once in a while for items that I no longer have a use for. For example, I used to decorate wedding cakes, but can't seem to find the time anymore. So I listed my decorating equipment - and boy, did it sell well.
I used to have this thing about keeping every book I read. Well, no more. I have parted with all of my books - afterall, they really only collect dust since I'm the only person who seems to read anymore. Once you've read a book, you're not going to read it again, well not for some time anyway. And although books look great if you have thousands nicely presented in a floor to ceiling bookcase - let's face it, making some money back on them is very nice also.
Garage sales are always a source of amusement. Most people just want to get rid of their "junk". You will often come away from garage sales after paying little more than $10 with $200 or $300 worth of "ebay stock".
There are plenty of liquidation sites, and auctions (physical not internet) where you will pick up total bargains ideal for retail.
I constantly scan the bulk lots or wholesale items on many of the auction sites. Then I separate into individual items and resell.
Without meaning to sound like a scab, I also ask my friends to give me their discarded clothing that would normally go to the Good Sammys or St. Vincent de Paul. I recently had a friend who was moving house and was talking about needing to donate excess clothing, ornaments, computer equipment. I said - well, before you do that, let me go through it in case I can use something you're giving away - hence another mountain of ebay stock.
Truly, ebay stock does not have to be new and on many occasions, it doesn't even have to be in perfect condition. Sometimes, people will buy a broken computer - because it may only be the motherboard that isn't working. Possibly the processor, ram, drives etc are all in perfect working order.
Roadside pick up can also yield many items for ebay stock.
Once you start really looking, you'll be amazed how every sale, every store closure - has an opportunity for gathering ebay stock.