I too have tried in the past to get small fixings similar to what you are looking for, I rarely have any success.
There are a vast range of small threaded fastening used nowadays in small consumer products, its hard to believe that they are all bespoke but that probably is the case. I think that the high volume product manufacturers design, and then have made a range of fastenings tailored to their products.
My best suggestion for your screws would be to include the word 'Micro' in your searches, as in 'microscrews, micro fastenings' etc. For some reason sizes below about 2mm are regarded as being specialist.
Ian