Okay, I know it's an old thread but a question must be answered!
The only hex-section styrene rod I've found is from Plastruct (as suggested in an earlier post)...
90872 0.8mm
90873 1.0mm
90874 1.5mm
90875 2.0mm
90876 2.5mm
90877 3.2mm
I bought a packet of each size from Hiroboy here in the UK back when I started the 908, but although they're still listed on the site, they're all out of stock. Must be someone else out there selling it...try searching these numbers and see what comes up.
SB