Try a local garden store, or a big box store, or even one of the nationwide "marts", for an orchid bark mix. You can also look on line for orchid media. If the bark mix you get seems to you to have too many big chunks, cut up some of the sphag and mix it with the bark. I'm sure others will have more suggestions for you. What is the air circulation like in the area you have your orchid? More circulation would help the sphag dry faster.