Where to buy reverse adapter???

for my Sigma 10-20 for Macro... I've looked around but I don't know what size I should be looking for

I tried to read up on it but I'm really confused as to how it works... I just am looking for a cheap/fun way to do some macro

Cheap/fun way = extension tubes. Slap those silly things onto your 70-200L and you'll be taking macros like a pro! haha

Thanks for the advice... the only issue is the extension tubes cost nearly 10x what the reverse adapter costs

Im pretty sure hvstar.com has them...

But with a reversing adapter, unless you use a manual focus manual aperture lens, you will have no diaphram control so you cannot easily focus wide open and then stop down the aperture to take the shot.