12" of platinum anode material from anomet. The price is about $20 USD a foot for the .188" diameter

Farwest Corrosion Control (http://www.farwst.com) can supply these and more. 3 feet of ELGARD 3mm wire anode (DSA - copper core, titanium inner layer, 'mixed metal' oxide outer layer) for 12.95 per foot.

since platinum should be used between 200 and 600 ma/cm^2 the more surface area the better (the 0.188"dia is better than 3mm)