Why not try foraging something like willow? You could then bend the twigs into anything that you think would provide mental stimulation and also being a healthy treat at the same time.
I love the idea of foraging but I don't think I'd have a clue where to start, I'm not very outdoorsy! I'd hate to pick the wrong things for them!
They only seemed interested in chewing things they shouldn't be the last few days like their litter tray and the skirting boards even though their safe things for chewing are right next to them!
Perhaps you could pop along to a forthcoming RU meeting at Croome Court near Pershore,(date(s) still to be decided in Feb/March) and have a chat with other fellow bunny mad folk. Tea, coffee. lovely food and bunny chat......:thumb:
Have you tried putting herbs/veg/pellets into a paper bag and mixing it up with hay? My 2 go mad for that throwing the bag around like lunatics :lol: they always destroy the bag too after eating the contents...keeps them busy for a few minutes :roll:
ETA I forgot about this sticky http://forums.rabbitrehome.org.uk/showthread.php?303726-Rabbit-toy-making-and-enrichment-activities there might be some useful things on there :wave: