Hello @uda2684
Yes you can. Usually it would be peer to peer transaction if you find some one who wants to sell you ADA. Also, you need to trust that person. You can use your PayPal or E-transfer to buy from individuals.
If you go on eBay and search under ADA “Mining” contracts you may even be able to use a Credit Card. They call them mining contract leases since they can sell service on eBay but they can’t sell crypto.
Keep in mind that price will be higher due to 10% to 14% eBay and PayPal/Credit Card processing fees as well as mark up. Here are some examples:
Centralized exchange is just easier and way cheaper, until enough people adapt crypto, then you’ll be able to get it anywhere. For now, not enough people have and use crypto in their daily life to warrant any investment into wide spread OTC exchange.