I don't usually use the INFILE statement or deal with binary files, but I think the process is exactly the same as for the DATA step. Remember that you can call most Base SAS functions from SAS/IML. In particular, you can call the FINFO function and other file-related functions. Adapting the doc example to IML gives:
filename fref "C:\temp\myfile";
proc iml;
fid=fopen('fref');
/* for my OS, what FINFO options are available? */
infonum=foptnum(fid);
infoname = foptname(fid, 1:infonum);
print infoname;
/* looks like the 4th element is the file size on Windows */
size = finfo(fid, infoname[4]);
print size;
close=fclose(fid);