I presume that you're talking about something to cover the wire to make it actually look plant-like?
I'm strictly a beginner, but have you looked at florist's tape?
It's a roll of plastic-looking tape, which you can stretch to make thinner. It's self-adhesive (adheres to itself), and has a kind of waxy texture and property such that you can smooth it down along the stem wire and sort of "sculpt" it.
I've only found mid-green locally (Oz), but I'm sure you can get different colours from the WWW.
There was a website that sold supplies specifically for beaded flowers, but I can't find the link. I've also never bought from them, so I don't know what the service is like...
You might like to check these sites out though: