Yes there are. Ford Motorsports, Racer Walsh, Esslinger, Crane, Wolverine. Many to choose from. Keep in mind - with Speed Density systems, they don't like too big of cam. This also the same if you have a auto (vacuum issues).
The '91 has a MAF so the speed density issues aren't a problem. Vacuum issues on high lift, tight separation, cams will still be something to consider with an auto trans and/or power brakes.
Pay attention when cam shopping. The '91 valvetrain is hydraulic roller and most, but not all aftermarket cams are made for the older slider type followers. You can't use roller followers on a slider cam and vice versa. You can swap the cam and followers out as a package, i.e. slider cam and followers replacing a roller cam and followers or the other way around.
Roller cam choices are limited, The FRPP A237 cam is hydraulic roller as is one of the new Crane grinds. The new Crane is simply an A237 with the timing events moved 2 degrees. lift, duration, and separation are the same.
Just about every major cam manufacturer has something for a 2.3 but more often than not it's flat tappet (slider) rather than roller.
Be sure to pick a cam that fits your application. A cam that calls for super high compression or has a power range outside of your normal operating range in an otherwise stock motor won't perform well at all. Sure it may sound cool at idle, but that's where the fun ends.
Something else to consider would be an adjustable cam gear. Sometimes moving the cam timing a couple of degrees advanced or retarded can improve performance. There won't be an increase in power, you'll just be moving the hp/tq curve to suit your needs/wants. It's a cheaper initial investment over an aftermarket cam and if you decide that you still want more, you can then use the gear on your bigger cam to move the curve around.
You see where he said "Ford Motorsports, Racer Walsh, Esslinger, Crane, Wolverine" above? If you plug those into www.google.com , it will give you their web addresses...