I have no idea of cricket (other than some scenes from British movies that didn't help me in any way understanding the rules) and I'm not sure what a bowler does so I don't know how these translate but I do some gripping exercises for martial arts and use basically homemade tools for this.
The easiest to build is a tennis ball. I have one in my office and one at home and just squeeze them. It's the same principle as grippers (spring loaded) but much cheaper.
The other thing I often use is a wrist roller. It's easy to construct since it's one a weight on a string on a stick. So what you do with it is you hold the stick and twist it to wrap the string around the handle to bring the weight up and down. That's basically a wrist exercise but also works hands and fingers.
An other thing that seems to be popular for grip strength are clubs but I haven't tried that so I can't tell you much about them.
What also works for pinching strength is just grip some weight with your pinched fingers so for example grab a filled bottle of water or a dumbbell plate with you fingers by the rim but in a way that you only hold it by pinching you fingers (so no hooking the tip of fingers under a rim or anything) and hold it for a while.
Not sure if that helps or if the Sri Lankan army does any of this.
Edit after clarification:
I don't know of any tool that does provide resistance in a flicking direction. The two options I can think of to add resistance in an outward direction are either to do that motion against a rubber band (which will most likely fly off into your face if you don't find a way to attach it somehow so it can't get off your fingers (maybe sew it to an old glove)). Or do the movement in something like a bowl of sand (wearing gloves if you don't also want to condition your skin) or something similar (high viscosity liquid or something) to add resistance to the movement.
Found a few links on the extension topic: Here is one mentioning a commercial tool for this kind of excercise and showing how to replace it with a piece of thera-band. This one shows an easy way to fix a rubber band for resistance. And here is one realy adding anything new but mentioning the sand bowl method which was just a wild stab in the dark.
I tried the thera band thing and I have to say I have very unbalanced gripping and extension strength...