You absolutely can buy seeds. I have many times, never had a problem. If your shipment does happen to get intercepted by customs, you will just get a scolding letter in the package instead. If you pay the extra $10-12 for "stealth" shipping, they will reship it if that happens. I never had it happen though.
The best way to start out is seeds, imo. You avoid the headaches of strange clones (uncertain genetics, mites, disease), and you build up a seed library for later, for trading, etc.
I like The Attitude seed bank myself. Tons of freebies with every order, and there is a promotion nearly every month, big promotions every few months. Go to their web site and get on the mailing list.
There are plenty of reputable sites also, but Attitude is the one I use:
https://www.cannabis-seeds-bank.co.uk/