I buy huge cork slabs, 40 lbs. (or more) of them at a time. I have a tiny tropical plant business and cut the cork slabs to whatever size a customer asks for.
You can use the silicone sealant sold for use as a tillandsia "glue", but that works best for pretty small plants. I sometimes will use that glue but supplement it by using plastic-coated, florist wire. I will drill two holes adjacent to and on both sides of the roots and then two more holes further up the plant. The wire holds the roots against the cork until their roots take hold and the upper two holes hold the plant upright. For staghorns, orchids, bromeliads, and most tillandsia, I just use the florist wire. I posted a "how to mount epiphytic plants" on ATP last January. You might get some helpful information from that post.
