When I was trying to upload MinION data to SRA, they wouldn't allow me to upload only the raw signal data (i.e. FAST5 files). Every file needed to contain a FASTQ sequence, and this sequence was extracted from the file and stored in the archive. Given this, I don't expect it will be possible to retrieve signal or event information from SRA. I also don't expect this will be possible in the future either, given that the SRA database expects every record to have a FASTQ-like sequence attached.
However, EBI/ENA do allow the upload of raw FAST5 files to the database (e.g. here), but there are no FAST5 reads for the specific single-cell B1a study you have indicated. If you're interested specifically in that study, then I recommend that you ask Miten Jain directly for access to those reads; he should have another method to give you access to them.
ENA is "ready" for ONT reads, but researchers need to upload their reads to ENA in order for that database to be useful.