Long division is primarily a mechanical set of rules so you don't need any online apps to generate problems. Just pick some random numbers to generate the initial number and then afterwards the divisor. When I was teaching it to my son, I had him pick a digit and then I did the next one until we generated a large enough practice number.
To do multi-digit divisors one should be comfortable with ballpark estimating multiples and if not that should be practiced first as a standalone activity.
That being said, I think you'd be best off doing an explanation of why the std algorithm works as well and build up to it. A digression into the associate/commutative and distributive properties are useful here.
Ben
