Last rods I bought were from Welding Supplies and Welding Equipment | Plasma Cutters | TIG Welder, MIG Welder, as they were the cheapest I could find for LoHy (7018 IIRC) rods.

I usually just google for what I'm looking for, and compare. I've bought from several places in the past, with the biggest issue being knowing what you're looking for.

Anything specific you're needing?