For those who may happen to reach this thread by way of search in future you can convert a fasta file to fastq format using
reformat.sh from BBMap suite.
Please remember that the Q-scores created here are fake (example below sets Q-scores to 35 for all bases).
reformat.sh in=test.fa out=fake.fq qfake=35
FASTQ has more information content than FASTA. The conversion would require that you add some kind of quality scores, most probably some dummy values.
What would really enable us help you better is knowing the purpose behind your quest.