Marble Branch Farms and Carter & Holmes usually give me freebies even when I only order 2 or 3 plants. Marble Branch gives out particularly nice bonus plants; I've gotten Cattleya cernua x Laelia anceps, Rhynchovola David Sander, Broughtonia sanguinea, Dendrobium Kokomo, and a few others over the last few years... Their freeness with freebies is definitely one reason they're high in my 'favorite vendors' list.
I have a grower I buy from that has not charged me for a few plants out of an order. An other grower has not charged me postage on one of my last orders!
Kawamoto has sent me free plants, I think when I was a new customer. Another vendor sent me a freebe when he had to delay shipping for some reason. I also got a free Platycerium elisii because the vendor delayed the shipping so long I had to complain to eBay. And I'm sure I have gotten others too.
Beverly A.