I found this picture of a mounted Oncidium. I reccommend mounting orchids on cork or grapewood, as this is how they grow naturally. Easy to do!
Buy a small yearling orchid from your local grower, remove all 'soil' (should mostly be wood chips), wrap lightly in some dry green moss, and mount directly to your cork wood, using strong fishing line to secure until roots take hold. I also mount tillies or spanish moss with my orchids, makes for a very pleasant composition. Added bonus: my chameleons seem to LOVE resting on my mounted orchids (especially Jacksons!).
The link I included is for Pacific Orchid in Valley Center, CA where I used to buy my orchids wholesale (back when I ran my own bonsai nursery!). Great selection of orchids! Check em out!

Pacific Orchid Website
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Victor Gomez
gomezvi.tripod.com/sdchamkeepers/
gomezvi@yahoo.com