I assume by “being an introvert” you mean you have social anxiety. If so, start out by looking for things you need online, followed by your location. Many local businesses will have some kind of online presence, or at least a Facebook page. Check what businesses those pages follow or interact with. At least that way you’ll gain some background.

Buying local is ideally going to be a more social experience. You will start having to seek out local markets and meeting the people who provide their goods and services. You’ll also find it easier once you visit local places For example, the local brewery here hosts markets. Local supermarkets buy food from (relatively large) local farms. Smaller local farms work directly with local restaurants. It’s all interconnected.

Depends on your area mostly. Look for local signage based around yard sales, flea markets and farmers markets. Tons of times I’ve found local product makers at one of the three. Facebook marketplace is also a good place to find local businesses.

Craigslist/fb marketplace can be a good way to find garage sales so you dont have to negotiate a meet up time / place or anything. Also look for estate / moving sales. Check along local roads for signs on upcoming garage sales.

Thrift stores can be ok but can be expensive or not have great stuff if its in an expensive area. Consider going to smaller shops / delis and looking for if they have a section for local business cards; some places will have a section where people will leave a stack of business cards, so you might be able to find smaller thrift/antique shops that way, or find an ad someone has left for upcoming sales.

Also check: local facebook groups, local library in person / website

Not sure about other online sites or specific items though.