Many shopowners are willing to discuss general business conditions and their inductry in general with others who will take the time to listen. Knowing a few "keywords" and industry specific terms will help, but you can get quite a bit of information out of store owners if approached in the right way. Making it clear that you are not going to open around the corner also helps.
As far as getting any specific sources, you won't do well, but there are ways.
There is my patented "dumpster diving sources determination method". Here are a number of things you can do with any type of retail business you want to get some supplier information on.
1 - Pick up the goods on display and make a note of the manufacturers / importers / whatever name is on the package. You can often contact that company, tell them you are interested in
opening a shop (do not say website) and would like to know a) if the sell direct to retailers or b) the names of some distributors you might contact.
2 - Watch for delivery trucks to the business and note any names / phone numbers on the sides of the trucks. Contact those companies.
3 - Look for any "trade literature" (magazines, newspapers) that might be lying around. Many of these have "bingo cards" in them which allow you to order a subscription to the pubilcation and / or circle numbers tied to specific ads in the publication so that the company placing the ad will mail you information on their products.
3A - This will also place you on additional mail lists. You will become a "store" to many companies, even if you don't own one. On the bingo card will be qestions about your business, how many employees, how much $$ volume, what is your position, etc. Make up some answers. You hav 5 employees, do $ 500,000 per year and you are the president, etc.
3B - These subscriptions are free. Once a year you'll get a card asking that you verify you are receiving the publication, as they charge their advertising fees depending on their 'audited" numebr of subscribers.
4 - Ask to use the restroom in the shop if it is in the back. Snoop around on your way to and from, noting names on shipping labels. Contact the shippers as above.
5 - Check out the dumpster. You will often find cartons with shipping labels attached. Contact those shippers as above.
6 - Chat up any employees. Many are there just for the paycheck and may be willing to share some trade secrets with you.
Finally, if you run into an owner who is totally hostile, wait until he is not there, then go back to the shop and say soemthing like 'Has Sam sold the shop yet? Last time I talked to him he said he was losing his butt and he was going to sell by the end of the month." That should create a few problems for him.

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