At EBI-ENA or NCBI-SRA.

You could try the NIAID Data Ecosystem: https://data.niaid.nih.gov/

It's designed to help researchers find datasets from infectious and immune-mediated disease studies and there are tons of transcriptomics datasets. You can try a very specific search like "miRNA cDNA expression liquid biopsy" and get a few results or try a little broader like "liquid biopsy" and then narrow down the results by Measurement Technique, Health Condition, or even Source. Hope that's helpful in the future!