Mike,
Dave bean has a spring kit for $8. I know because I just ordered one this week. You can also shim the spring to get more pressure, but I'd rather pay $8 so I don't have to take it apart again if it's wrong. I figure I'll put it in if I ever decide to sell it - so the prospective buyer isn't concerned with the oil pressure.
The spring is accessed from the block side of the pump. If you buy bean's spring, they'll send you a catalog that has exploded views.
Keep in mind, there's nothing wrong with 5psi idle/ 25psi 3000 rpm. The crossflow likes good flow, not necessarily pressure. Formula Fords run these pressures all day (and the ones running the lower pressures make more power). Another thing to consider is more pressure may mean more oil leaks...