You can get BAM files for 10x single-cell data and they can be found under the Data Access tab of the SRA record under the Original Format section (when submitted). Here is one example : https://trace.ncbi.nlm.nih.gov/Traces/?view=run_browser&acc=SRR24503270&display=data-access

For most other samples you are going to need to align the data and create the BAM files yourself.