It is almost impossible to control or rid this pest. In your place I would be making the decision to discard all infested orchids and to keep a close eye on the ones that at the present time don't seem infested. When buying new ones check each plant from top to bottom for scale.

I have had this problem in the past and have used methelated spirit with some success. However this is ok for 1 or 2 orchids beyond that I agree with Loosestrife2. Life is to short, chuck them and start again

Use a cotton bud dipped in meths. and wipe off the scale.

Thank you I have never heard of this before and will certainly give it a try.