Old Country Gardens ~ They are very nice!

google it

My brother-in-law once potted a Japanese Maple from my yard with the intent to bonsai. He was pulled over driving home because it looked like something else.

I do bonsai. Started a few years ago. As far as I know there isn't anywhere in Delaware that sells anything that would be considered a decent bonsai that I'd spend money one. Nor is there any type of society or club to join like most states and cities. You have to read and learn as you go. I can direct you to several websites to order bonsai. Range from $350.00-$5,000+
Most pre-bonsai of any quality goes for $100-$200 and still requires years of work to fill it out.

I think Longwood does in their gift shop.

Concord nall on 202 there's a store in there that sells all those exquisite plants! Hooah!

There was a vendor today at the Riverfront Holiday festival! I didn't pick up a card though. Perhaps if you leave a message at Holiday Food & Gift Festival the organizer can put you in touch with them.