Hi-volume oil pumps are not necessary in the average street driven I6. Maybe in an engine cranking 6 - 8k+rpm for long periods of time (NASCAR, F1, CART, IRL, etc.) where keeping journals and bearings cool is essential to longevity, but not a daily driver street car. As long as you have 10psi per 1000rpm, that's sufficient pressure to keep things happy. Even if one were available, personally, I'd never use one with the stock capacity oil pan.
Follow Jack's advice if you need to increase oil pressure. Remember, if you have low oil pressure, and you know your oil pump is in good condition, then you have too much bearing clearance. Shimming a known good pump and/or using a hi-volume pump won't fix that.