Here are some ideas, and I hope they help.
Listen to other instruments playing rolls, like accordion, pipes and fiddles to take you out of just the whistle context. Find a tune that you REALLY just have to learn to play and want to sound just like that instrumentalist. I did it with a Bobby Gardiner accordion cd and Fermoy Lasses. Later, I found several fiddle versions that just made me want to be part of the party!!
Once you have the solid sound in your mind, go back and follow the information given by BrotherSteve or spring for the Grey Larsen book, which is worth every cent because he tells you EXACTLY how to achieve rolls, first by learning cuts and strikes. If you do the exercises, by the time you get to his roll chapter, you can already do the necessary fingerings. Its a clever approach. Whereas Steve teaches you on the roll itself, and the DABLABLA method, Larsen preps you into it. They are both valid and useful ways. I learned from the BSteve method and only recently purchased the Larsen book, somewhat out of curiosity and also to get the master’s soloes. I really think that Larsen spent many, many hours pondering how to best teach things and there are many extras in the book that Steve could not practically cover in a website, even though he is well aware of the things that Larsen describes.
BSteve is the best free way to learn. With the Larsen, there are many more recorded examples because he was able to do that in a for-profit project. he handles every contingency, like getting from various scale notes to others and achieving the cuts etc.
One caveat is that he differs on which finger to use for the cuts from BSteve and others. Now, the way I see it, if you can learn EITHER and get good at it, you will have the ability to change later (but you will spend some time re-training). I think Larsen is in the minority with his finger-above system, but I have to say that it works for me okay even though I was trained the more popular way. I have some lingering doubts with his system which are too complicated to explain here about certain fingering combos with the cuts.
The problem I had with rolls, once I UNDERSTOOD what they were exactly, was usually with the lower finger “tap” or “strike” or whatever lingo you use. And usually, it was with either of my third fingers, which are anatomically slower than your index and middle because they are tied to the pinky by tendons. I experimented with distance from the hole, not always covering the entire hole etc etc. By experimentation, you find something that works, even if you eventually change, which I did. At first, I was tapping very lightly to gain control of the lift of that tap finger. Now I can hit it more vigorously, because the finger is trained. Remember that this is like a finger gymnastic exercise, that will only work with training and time, combined with determination to get it and a musical model in mind of how it should sound.
Good luck!!