I have the TBC-2501 trimmer. It's lightweight and very powerful. But in order to save time, I'd like to buy another head for it so that we can keep one with string ready to go. I know I should just buy another trimmer but that's just not in the budget yet. I think this trimmer comes with the 5" head? My question is, where can I buy another Tanaka 5" head to keep as a spare?