Give your vet a call. He/she should be able to provide you with both a syringe and some medically sound advice on how to encourage your bun to eat.
Some practical advice... just keep trying different greens. Below is a list (stolen from
www.3bunnies.org, a favorite rescue in my area) of greens that are safe and good for bunnies to eat.
Alfalfa sprouts
Apple Mint
Basil
Beet Greens
Bok Choy (Chinese cabbage)
Broccoli leaves and stems (Note: broccoli can cause gas in some bunnies, and it is high in calcium, so it should not be given to bunnies who have any urinary tract problems, such as bladder sludge)
Brussels sprouts
Carrot tops
Celery (especially the leaf) (Note: to avoid any potential problems, slice or chop the celery against the grain so the veins aren't stringy - veins can be swallowed without proper chewing and can cause serious gastrointestinal problems)
Chard
Cilantro (no roots)
Clover & clover sprouts
Collard greens
Dandelion greens & flowers
Dill
Endive
Escarole
Fennel
Green pepper
Lettuce: romaine (only limited amounts, may cause excess cecals), green leaf, red leaf (no iceberg)
Mint
Mustard greens
Parsley
Peapods (flat)
Peppermint leaves
Pineapple-mint
Pineapple-sage
Radicchio
Radish sprouts & tops
Raspberry leaves
Sweet potatoes
Turnip greens (tops)
Watercress
Wheat grass
I've learned from trial and error that there are some greens on that list that Chomper will simply inhale and others that she'll eat reluctantly and only when she's really hungry.
Good luck!