Datasets for generating longer summaries

I was looking into generating summaries for big articles (3-4k tokens) using Longformer (summary length 200-300 token). I tried using this model by @patrickvonplaten . Since it was trained CNN/Daily mail the summaries are pretty small (3-4 lines). I was going to fine-tune to generate longer summaries. Are there any such datasets that have bigger summaries? I took a look at datasets listed here but could not find anything.

If there aren’t any datasets like this what are some other strategies that I can use? Filter out the shorter summaries and only use the big ones?