Check Sigma and Goodfellow. See the example below:
Commercially available polyethylene (PE) particles of different size classes: 40–48 μm (average size, ultra-high molecular weight powder, CAS No. 9002-88-4, Sigma-Aldrich UK); 125 μm (average size, ultra-high molecular weight powder, CAS Number 9002-88-4, Sigma-Aldrich UK) and 350 μm (average size, medium density polyethylene powder, CAS 708-316-83, Goodfellow).