I'm not familiar with a product like that. I have seen people use wire wrap, small glass "apothecary-style" bottles, cast pewter dragon claws, etc to hold a variety of shapes.
I know of an australian Company that sells a silver cage that you can hold crystals in it.. you can change them when you feel you either need a combination or a different crystal.. They also sell on ebay as well
they are called Earthmade..I 100% recommend this company, I have been dealing on a wholesale basis with them for over 2 years.. and their products are high quality at low prices. they post overseas.
They actually have one for sale on ebay right now..
They are all open "scrollwork" style. But you might be able to wrap a bit of organza or cheesecloth around the herbs/dried petals. Just be sure of the size before you buy.
Fire Mountain Gems is a jewelry-making supplies company in the USA. It might make shipping a bit pricy for you, but you can try. Are there any shops near you that sell beads and findings for jewelry? Perhaps one of them could place the order for you when they are restocking.