As this is a batch file, and is only written once, there's little need to try to make your command as short as possible. Therefore just use one dir command and one echo command, instead of the currently accepted answer which essentially runs ten if commands, potentially nine set commands, and one echo command.
@Dir "filepath\a1*" "filepath\a2*" "filepath\a3*" "filepath\a4*" "filepath\a5*" "filepath\a6*" "filepath\a7*" "filepath\a8*" "filepath\a9*" /B /A:-D 2>NUL 1>&2 && Echo Yes
As filepath is constant, you could even do it like this:
@CD /D "filepath" 2>NUL && (Dir a1* a2* a3* a4* a5* a6* a7* a8* a9* /B /A:-D 2>NUL 1>&2 && Echo Yes)
Please note however, that your question is not clear enough to determine your full task. This example will print Yes if a[123456789]… exists in filepath, it will do that regardless of whether a file named a0… also exists in filepath.