This might be more expensive, but can help in a pinch. Buy some iron supplement pills and crush them up as finely as possible. Then, sprinkle them over the root system of your plant. You can even mix some in water and spray on the plant directly.

Look for a pill with Iron (Ferrous Sulfate). Ferrous Sulfate is the best type of iron pill I have found for your purposes. If you can, find the pills that come in the cheap capsules because you can just PULL these apart and sprinkle what is inside out without having to crush it. Here is another type to look for:

Each Vegicap® contains 25mg of Iron, as Iron Bisglycinate, which is a unique form of chelated iron formulated for maximum absorption without the gastrointestinal irritation or the constipating effects that often accompany iron supplements.

EXAMPLE: http://www.amazon.com/Solgar-Gentle-.../dp/B00013Z0QA
IRON SULFATE FOR PLANTS: http://www.amazon.com/Bonide-920-4LB..._bxgy_ol_img_b

If you can buy online though, you of course should just buy the liquid iron.
http://www.amazon.com/Bonide-Product...890215&sr=8-11