After doing a little checking, the only orchid plant I could come up with that had Tiger's Paw as the grex name is Grammatophyllum Tiger's Paw. The plant looks similar to the one you have pictured, and the growths are relatively large, the pseudobulbs on Grams can be two or three times the size of those on Oncidiums.
Here's a possible pic of the flower; it's the first bloom shown on the top right. It fits your description: does it look like what you remember?
As far as getting rid of the algae on your mount, that's going to be difficult. A product called RD-20 which is commonly used here as a bactericide and fungicide is also a good algicide, but I don't know if it's available in Hong Kong. I don't think the algae looks bad, though, so you might just leave it as is....