[susan53]

V+ing is fine immediately after I find.. with the adjective phrase at the end :

I find doing gymnastics really easy
I find doing gymnastics really boring
I find doing gymnastics extremely painful

But after I find it + adjective, the to + infinitive structure is more normal :
I find it really easy/boring/painful to do gymnastics.

Here are some authentic examples from the two corpora - one British English and the other American :

For my part I find it difficult to conceive such a state of affairs.
I find it, find it hard to believe that you're not...
I find it better to do all artwork at the finished size...
We often find it more useful to tidy that definition up
...which the Europeans may find it economically profitable to destroy
the student of literature may sometimes FIND IT helpful to classify a poem or an essay as...

and there were many more examples. The only example I found of the Ving construction used after it + adjective was :

I didn't find it dangerous living in the flats.

So it's possible, but much rarer than the infinitive construction.