according to nookipedia, blue roses are the result of hybridizing two 1110 hybrid red roses, which are produced by cross-breeding a yellow rose with a 1011 hybrid pink flower.
You can get a 1011 hybrid pink rose from cross-breeding a store-bought red rose (2001) and a purple rose. There is also a chance that you get a 1011 hybrid pink rose from breeding store-bought red and white roses.
Here is the chart from Nookipedia:
It's not clear to me whether this is accurate, however - I have successfully bred each of these necessary roses, and so far none of the 1110 hybrid red roses have produced a blue rose ... They have produced more black, white, and red roses, however.
Maybe it's just a matter of time, since the blue rose is a 1.56% chance ...
Pretty sure you're on the right track. The chances are just very low, as you can see. You might be interested in this page with strategies: https://yuexr.github.io/acnh/bluerose
Based on the Nookipedia chart, I followed the equivalent of the Asteriation 4-Step Method. I'm just at the end with several hybrid
1110red roses and no blue yet ๐ค Sounds like it's just a matter of time, glad to confirm this is the method others are using.