I've looked around for the metal rods too. I don't mind paying for them as I know they'll last and do the business, but haven't been able to find them so far. I did find these
Panda Stix the recycled plastic rot-proof plant support but haven't met anyone who has used them and if they're bendy etc. (plus the cost - not worked out in my head if they're pricey or good value??
Panda Stix special offers direct from the manufacturer).