In this paper, you can find a list of SRA accessions for Drosophila short reads. They have also provided the statisitcs for different de-novo assemblers: Optimizing de novo transcriptome assembly from short-read RNA-Seq data: a comparative study. Unfortunately, they do not seem to provide the assembled transcripts. I imagine that for D. melanogaster it is probably rare that researchers would be doing de-novo transcript assembly as there is a very good genome to assemble to.