The centro virtual Cervantes offers some readings divided into levels:
After you click on a level: inicial, intermedio, avanzado, you can click on one of the titles of the books and then select “texto”. In the text there’s a “texto para imprimir” button that would make it easier for you to import it into lingq.
I’ve also found this novel in pdf. I haven’t read it but it sounds interesting. You can convert the pdf into txt format using Calibre or an online converter to import it into Lingq. I’m sure there must be other material like that. Google for “lecturas graduadas español para extranjeros”