Tarozzi make a variety of raised, adjustable clip ons. Disco volante sells them. Flat racer used to sell them but I'm not sure now. They are around £100 I think.
I've seen some Chinese made cnc raised, adjustable clip ons on e bay. Look very nice and cheap, but my big worry with those is that there are two joints per bar and with the leverage I'd be concerned about them moving. Maybe you could modify them although there looks to be little material.