Carlwen once made a line of fluid-mount carriers, which still sometimes turn up in battered condition.
Any competent machine shop with CNC could make you a set. It's the best way to supress rings & dust.
At this level of precision, you'd want plano-perfect optical glass to avoid secondary reflections. I never
went for it due to all the potential mess and cleanup headaches. If you can't get glass clean now, spending a thousand bucks on a custom carrier isn't going to change anything.