Finding Rna-Seq dataset for C. Elegans (Caenorhabditis elegans)
Go to NCBI-SRA or GEO and search for RNAseq data. Set organism as C. elegans and optionally any other keywords that you are interested in. This search term will give you all RNAseq data in SRA from C. elegans: ("caenorhabditis elegans"[Organism]) AND "strategy rna seq"[Properties] 

You will generally find files in fastq format which you can easily convert to fasta. There are many tools that do that; you can also do it with your own script. Following awk command will do the job:

awk 'NR%4==1{print "&gt;"substr($0,2)} NR%4==2{print}' data.fastq &gt; data.fasta

Apart from SRA you can also look at ENA (European Nucleotide Archive) and DDBJ