If you have a friend or someone in your family that is really into gardening, or even into floral designing, your local garden center or local florist may be a great source for those hard-to-find stocking stuffers. Just think of a bag or wicker basket filled with all kinds of gardening needs for next spring such as fertilizers (general purpose-water soluble, lime, bone meal, blood meal, slow release, etc.), fungicides both liquid and granule as well as an assortment of insecticides. How about a garden hose and a high quality watering wand with a deluxe water breaker.
All gardening enthusiasts need an assortment of pots and of course, all kinds of soils. There are general purpose potting soils made without real dirt (soiless mix), then, there are soils blended specifically for African violets, orchids, cactus and amendments such as vermiculite and perelite. Natural amendments for your outside garden soil might include top soil, peat moss (both Michigan and Canadian), sand and different types of compost (cow manure or mushroom compost-which I suspect is actually horse manure).
If you are a handyman and like to build gifts for Christmas, I might suggest building your gardening friend a nice potting bench---some place where they can spread out their soils and stack their pots and divide their bulbs and be just as messy as it takes to get the job done. I hear people talking over my shoulder all of the time saying, "Gee, I wish I had a potting area like this at home." Look online and in gardening magazines for ideas on how the bench should look. Oh, and another homemade project would be a cold frame so that the home gardener starting his own seedlings has a cool, but safe place to move the seedlings to in the early spring.
Now if your friend is more into floral designing and "crafting," then maybe inexpensive floral containers as well as styrofoam and "Oasis" (soft foam) would make a good gift. These items can be difficult to find as are styrofoam rings and crosses so a trip to your favorite florist may be the place to go. Other items that come to mind are fountains, birdbaths, hummingbird feeders, chimes, statues, stepping stones, little collectibles, concrete benches and memorial throws.