I'm trying to find a relief valve around the .187 diameter sizing.  I currently use a Lee Co. valve, but it doesn't function very well at the moment.  I'm looking for at least 200 psi cracking pressure.

You may try to clear up how its used in this application.  We have a volume that has only one input to be filled and a fairly complex shape and this Lee Co. valve inserted to allow the volume to vent if the pressure exceeds XXXpsi once the system is filled and closed.  But since there is only one input, you can't just pour in the oil, you have to pull a vacuum on the volume with a container of oil inline and let the oil backfill into the void.  It works very well until this valve doesn't seal after it has vented once.

If you could scale up just a skosh you could use a lubrication type relief valve.  The SAE fitting is to show the construction and the Alemite reference catalogue has a valve that will meet you pressure needs.  
All fitting manufactures have this type relief valve or some even have vent valves that have high cracking pressures

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